Class: Proc

Inherits:
Object show all
Defined in:
proc.c,
proc.c

Overview

A Proc object is an encapsulation of a block of code, which can be stored in a local variable, passed to a method or another Proc, and can be called. Proc is an essential concept in Ruby and a core of its functional programming features.

square = Proc.new {|x| x**2 }

square.call(3)  #=> 9
# shorthands:
square.(3)      #=> 9
square[3]       #=> 9

Proc objects are closures, meaning they remember and can use the entire context in which they were created.

def gen_times(factor)
  Proc.new {|n| n*factor } # remembers the value of factor at the moment of creation
end

times3 = gen_times(3)
times5 = gen_times(5)

times3.call(12)               #=> 36
times5.call(5)                #=> 25
times3.call(times5.call(4))   #=> 60

Creation

There are several methods to create a Proc

  • Use the Proc class constructor:

    proc1 = Proc.new {|x| x**2 }
    
  • Use the Kernel#proc method as a shorthand of Proc.new:

    proc2 = proc {|x| x**2 }
    
  • Receiving a block of code into proc argument (note the &):

    def make_proc(&block)
      block
    end
    
    proc3 = make_proc {|x| x**2 }
    
  • Construct a proc with lambda semantics using the Kernel#lambda method

(see below for explanations about lambdas):

   lambda1 = lambda {|x| x**2 }
  • Use the Lambda literal syntax (also constructs a proc with lambda semantics):

    lambda2 = ->(x) { x**2 }
    

Lambda and non-lambda semantics

Procs are coming in two flavors: lambda and non-lambda (regular procs). Differences are:

  • In lambdas, return and break means exit from this lambda;

  • In non-lambda procs, return means exit from embracing method

(and will throw +LocalJumpError+ if invoked outside the method);
  • In non-lambda procs, break means exit from the method which the block given for.

(and will throw +LocalJumpError+ if invoked after the method returns);
  • In lambdas, arguments are treated in the same way as in methods: strict,

with +ArgumentError+ for mismatching argument number,
and no additional argument processing;
  • Regular procs accept arguments more generously: missing arguments

are filled with +nil+, single Array arguments are deconstructed if the
proc has multiple arguments, and there is no error raised on extra
arguments.

Examples:

# +return+ in non-lambda proc, +b+, exits +m2+.
# (The block +{ return }+ is given for +m1+ and embraced by +m2+.)
$a = []; def m1(&b) b.call; $a << :m1 end; def m2() m1 { return }; $a << :m2 end; m2; p $a
#=> []

# +break+ in non-lambda proc, +b+, exits +m1+.
# (The block +{ break }+ is given for +m1+ and embraced by +m2+.)
$a = []; def m1(&b) b.call; $a << :m1 end; def m2() m1 { break }; $a << :m2 end; m2; p $a
#=> [:m2]

# +next+ in non-lambda proc, +b+, exits the block.
# (The block +{ next }+ is given for +m1+ and embraced by +m2+.)
$a = []; def m1(&b) b.call; $a << :m1 end; def m2() m1 { next }; $a << :m2 end; m2; p $a
#=> [:m1, :m2]

# Using +proc+ method changes the behavior as follows because
# The block is given for +proc+ method and embraced by +m2+.
$a = []; def m1(&b) b.call; $a << :m1 end; def m2() m1(&proc { return }); $a << :m2 end; m2; p $a
#=> []
$a = []; def m1(&b) b.call; $a << :m1 end; def m2() m1(&proc { break }); $a << :m2 end; m2; p $a
# break from proc-closure (LocalJumpError)
$a = []; def m1(&b) b.call; $a << :m1 end; def m2() m1(&proc { next }); $a << :m2 end; m2; p $a
#=> [:m1, :m2]

# +return+, +break+ and +next+ in the stubby lambda exits the block.
# (+lambda+ method behaves same.)
# (The block is given for stubby lambda syntax and embraced by +m2+.)
$a = []; def m1(&b) b.call; $a << :m1 end; def m2() m1(&-> { return }); $a << :m2 end; m2; p $a
#=> [:m1, :m2]
$a = []; def m1(&b) b.call; $a << :m1 end; def m2() m1(&-> { break }); $a << :m2 end; m2; p $a
#=> [:m1, :m2]
$a = []; def m1(&b) b.call; $a << :m1 end; def m2() m1(&-> { next }); $a << :m2 end; m2; p $a
#=> [:m1, :m2]

p = proc {|x, y| "x=#{x}, y=#{y}" }
p.call(1, 2)      #=> "x=1, y=2"
p.call([1, 2])    #=> "x=1, y=2", array deconstructed
p.call(1, 2, 8)   #=> "x=1, y=2", extra argument discarded
p.call(1)         #=> "x=1, y=", nil substituted instead of error

l = lambda {|x, y| "x=#{x}, y=#{y}" }
l.call(1, 2)      #=> "x=1, y=2"
l.call([1, 2])    # ArgumentError: wrong number of arguments (given 1, expected 2)
l.call(1, 2, 8)   # ArgumentError: wrong number of arguments (given 3, expected 2)
l.call(1)         # ArgumentError: wrong number of arguments (given 1, expected 2)

def test_return
  -> { return 3 }.call      # just returns from lambda into method body
  proc { return 4 }.call    # returns from method
  return 5
end

test_return # => 4, return from proc

Lambdas are useful as self-sufficient functions, in particular useful as arguments to higher-order functions, behaving exactly like Ruby methods.

Procs are useful for implementing iterators:

def test
  [[1, 2], [3, 4], [5, 6]].map {|a, b| return a if a + b > 10 }
                            #  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
end

Inside map, the block of code is treated as a regular (non-lambda) proc, which means that the internal arrays will be deconstructed to pairs of arguments, and return will exit from the method test. That would not be possible with a stricter lambda.

You can tell a lambda from a regular proc by using the #lambda? instance method.

Lambda semantics is typically preserved during the proc lifetime, including &-deconstruction to a block of code:

p = proc {|x, y| x }
l = lambda {|x, y| x }
[[1, 2], [3, 4]].map(&p) #=> [1, 3]
[[1, 2], [3, 4]].map(&l) # ArgumentError: wrong number of arguments (given 1, expected 2)

The only exception is dynamic method definition: even if defined by passing a non-lambda proc, methods still have normal semantics of argument checking.

class C
  define_method(:e, &proc {})
end
C.new.e(1,2)       #=> ArgumentError
C.new.method(:e).to_proc.lambda?   #=> true

This exception ensures that methods never have unusual argument passing conventions, and makes it easy to have wrappers defining methods that behave as usual.

class C
  def self.def2(name, &body)
    define_method(name, &body)
  end

  def2(:f) {}
end
C.new.f(1,2)       #=> ArgumentError

The wrapper def2 receives body as a non-lambda proc, yet defines a method which has normal semantics.

Conversion of other objects to procs

Any object that implements the to_proc method can be converted into a proc by the & operator, and therefore can be consumed by iterators.

class Greeter
  def initialize(greeting)
    @greeting = greeting
  end

  def to_proc
    proc {|name| "#{@greeting}, #{name}!" }
  end
end

hi = Greeter.new("Hi")
hey = Greeter.new("Hey")
["Bob", "Jane"].map(&hi)    #=> ["Hi, Bob!", "Hi, Jane!"]
["Bob", "Jane"].map(&hey)   #=> ["Hey, Bob!", "Hey, Jane!"]

Of the Ruby core classes, this method is implemented by Symbol, Method, and Hash.

:to_s.to_proc.call(1)           #=> "1"
[1, 2].map(&:to_s)              #=> ["1", "2"]

method(:puts).to_proc.call(1)   # prints 1
[1, 2].each(&method(:puts))     # prints 1, 2

{test: 1}.to_proc.call(:test)       #=> 1
%i[test many keys].map(&{test: 1})  #=> [1, nil, nil]

Orphaned Proc

return and break in a block exit a method. If a Proc object is generated from the block and the Proc object survives until the method is returned, return and break cannot work. In such case, return and break raises LocalJumpError. A Proc object in such situation is called as orphaned Proc object.

Note that the method to exit is different for return and break. There is a situation that orphaned for break but not orphaned for return.

def m1(&b) b.call end; def m2(); m1 { return } end; m2 # ok
def m1(&b) b.call end; def m2(); m1 { break } end; m2 # ok

def m1(&b) b end; def m2(); m1 { return }.call end; m2 # ok
def m1(&b) b end; def m2(); m1 { break }.call end; m2 # LocalJumpError

def m1(&b) b end; def m2(); m1 { return } end; m2.call # LocalJumpError
def m1(&b) b end; def m2(); m1 { break } end; m2.call # LocalJumpError

Since return and break exits the block itself in lambdas, lambdas cannot be orphaned.

Numbered parameters

Numbered parameters are implicitly defined block parameters intended to simplify writing short blocks:

# Explicit parameter:
%w[test me please].each { |str| puts str.upcase } # prints TEST, ME, PLEASE
(1..5).map { |i| i**2 } # => [1, 4, 9, 16, 25]

# Implicit parameter:
%w[test me please].each { puts _1.upcase } # prints TEST, ME, PLEASE
(1..5).map { _1**2 } # => [1, 4, 9, 16, 25]

Parameter names from _1 to _9 are supported:

[10, 20, 30].zip([40, 50, 60], [70, 80, 90]).map { _1 + _2 + _3 }
# => [120, 150, 180]

Though, it is advised to resort to them wisely, probably limiting yourself to _1 and _2, and to one-line blocks.

Numbered parameters can't be used together with explicitly named ones:

[10, 20, 30].map { |x| _1**2 }
# SyntaxError (ordinary parameter is defined)

To avoid conflicts, naming local variables or method arguments _1, _2 and so on, causes a warning.

_1 = 'test'
# warning: `_1' is reserved as numbered parameter

Using implicit numbered parameters affects block's arity:

p = proc { _1 + _2 }
l = lambda { _1 + _2 }
p.parameters     # => [[:opt, :_1], [:opt, :_2]]
p.arity          # => 2
l.parameters     # => [[:req, :_1], [:req, :_2]]
l.arity          # => 2

Blocks with numbered parameters can't be nested:

%w[test me].each { _1.each_char { p _1 } }
# SyntaxError (numbered parameter is already used in outer block here)
# %w[test me].each { _1.each_char { p _1 } }
#                    ^~

Numbered parameters were introduced in Ruby 2.7.

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.new {|...| ... } ⇒ Proc .newProc

Creates a new Proc object, bound to the current context. Proc::new may be called without a block only within a method with an attached block, in which case that block is converted to the Proc object.

def proc_from
  Proc.new
end
proc = proc_from { "hello" }
proc.call   #=> "hello"

Overloads:

  • .new {|...| ... } ⇒ Proc

    Yields:

    • (...)

    Returns:

  • .newProc

    Returns:


816
817
818
819
820
821
822
823
# File 'proc.c', line 816

static VALUE
rb_proc_s_new(int argc, VALUE *argv, VALUE klass)
{
    VALUE block = proc_new(klass, FALSE, FALSE);

    rb_obj_call_init_kw(block, argc, argv, RB_PASS_CALLED_KEYWORDS);
    return block;
}

Instance Method Details

#<<(g) ⇒ Proc

Returns a proc that is the composition of this proc and the given g. The returned proc takes a variable number of arguments, calls g with them then calls this proc with the result.

f = proc {|x| x * x }
g = proc {|x| x + x }
p (f << g).call(2) #=> 16

See Proc#>> for detailed explanations.

Returns:


3540
3541
3542
3543
3544
# File 'proc.c', line 3540

static VALUE
proc_compose_to_left(VALUE self, VALUE g)
{
    return rb_proc_compose_to_left(self, to_callable(g));
}

#==(other) ⇒ Boolean #eql?(other) ⇒ Boolean

Two proc are the same if, and only if, they were created from the same code block.

def return_block(&block)
  block
end

def pass_block_twice(&block)
  [return_block(&block), return_block(&block)]
end

block1, block2 = pass_block_twice { puts 'test' }
# Blocks might be instantiated into Proc's lazily, so they may, or may not,
# be the same object.
# But they are produced from the same code block, so they are equal
block1 == block2
#=> true

# Another Proc will never be equal, even if the code is the "same"
block1 == proc { puts 'test' }
#=> false

Overloads:

  • #==(other) ⇒ Boolean

    Returns:

    • (Boolean)
  • #eql?(other) ⇒ Boolean

    Returns:

    • (Boolean)

1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
# File 'proc.c', line 1302

static VALUE
proc_eq(VALUE self, VALUE other)
{
    const rb_proc_t *self_proc, *other_proc;
    const struct rb_block *self_block, *other_block;

    if (rb_obj_class(self) !=  rb_obj_class(other)) {
        return Qfalse;
    }

    GetProcPtr(self, self_proc);
    GetProcPtr(other, other_proc);

    if (self_proc->is_from_method != other_proc->is_from_method ||
            self_proc->is_lambda != other_proc->is_lambda) {
        return Qfalse;
    }

    self_block = &self_proc->block;
    other_block = &other_proc->block;

    if (vm_block_type(self_block) != vm_block_type(other_block)) {
        return Qfalse;
    }

    switch (vm_block_type(self_block)) {
      case block_type_iseq:
        if (self_block->as.captured.ep != \
                other_block->as.captured.ep ||
                self_block->as.captured.code.iseq != \
                other_block->as.captured.code.iseq) {
            return Qfalse;
        }
        break;
      case block_type_ifunc:
        if (self_block->as.captured.ep != \
                other_block->as.captured.ep ||
                self_block->as.captured.code.ifunc != \
                other_block->as.captured.code.ifunc) {
            return Qfalse;
        }
        break;
      case block_type_proc:
        if (self_block->as.proc != other_block->as.proc) {
            return Qfalse;
        }
        break;
      case block_type_symbol:
        if (self_block->as.symbol != other_block->as.symbol) {
            return Qfalse;
        }
        break;
    }

    return Qtrue;
}

#===(*args) ⇒ Object

call-seq:

proc === obj   -> result_of_proc

Invokes the block with obj as the proc's parameter like Proc#call. This allows a proc object to be the target of a when clause in a case statement.


944
945
946
947
948
# File 'proc.c', line 944

static VALUE
proc_call(int argc, VALUE *argv, VALUE procval)
{
    /* removed */
}

#>>(g) ⇒ Proc

Returns a proc that is the composition of this proc and the given g. The returned proc takes a variable number of arguments, calls this proc with them then calls g with the result.

f = proc {|x| x * x }
g = proc {|x| x + x }
p (f >> g).call(2) #=> 8

g could be other Proc, or Method, or any other object responding to call method:

class Parser
  def self.call(text)
     # ...some complicated parsing logic...
  end
end

pipeline = File.method(:read) >> Parser >> proc { |data| puts "data size: #{data.count}" }
pipeline.call('data.json')

See also Method#>> and Method#<<.

Returns:


3599
3600
3601
3602
3603
# File 'proc.c', line 3599

static VALUE
proc_compose_to_right(VALUE self, VALUE g)
{
    return rb_proc_compose_to_right(self, to_callable(g));
}

#[](*args) ⇒ Object

call-seq:

prc.call(params,...)   -> obj
prc[params,...]        -> obj
prc.(params,...)       -> obj
prc.yield(params,...)  -> obj

Invokes the block, setting the block's parameters to the values in params using something close to method calling semantics. Returns the value of the last expression evaluated in the block.

a_proc = Proc.new {|scalar, *values| values.map {|value| value*scalar } }
a_proc.call(9, 1, 2, 3)    #=> [9, 18, 27]
a_proc[9, 1, 2, 3]         #=> [9, 18, 27]
a_proc.(9, 1, 2, 3)        #=> [9, 18, 27]
a_proc.yield(9, 1, 2, 3)   #=> [9, 18, 27]

Note that prc.() invokes prc.call() with the parameters given. It's syntactic sugar to hide “call”.

For procs created using #lambda or ->() an error is generated if the wrong number of parameters are passed to the proc. For procs created using Proc.new or Kernel.proc, extra parameters are silently discarded and missing parameters are set to nil.

a_proc = proc {|a,b| [a,b] }
a_proc.call(1)   #=> [1, nil]

a_proc = lambda {|a,b| [a,b] }
a_proc.call(1)   # ArgumentError: wrong number of arguments (given 1, expected 2)

See also Proc#lambda?.


944
945
946
947
948
# File 'proc.c', line 944

static VALUE
proc_call(int argc, VALUE *argv, VALUE procval)
{
    /* removed */
}

#arityInteger

Returns the number of mandatory arguments. If the block is declared to take no arguments, returns 0. If the block is known to take exactly n arguments, returns n. If the block has optional arguments, returns -n-1, where n is the number of mandatory arguments, with the exception for blocks that are not lambdas and have only a finite number of optional arguments; in this latter case, returns n. Keyword arguments will be considered as a single additional argument, that argument being mandatory if any keyword argument is mandatory. A #proc with no argument declarations is the same as a block declaring || as its arguments.

proc {}.arity                  #=>  0
proc { || }.arity              #=>  0
proc { |a| }.arity             #=>  1
proc { |a, b| }.arity          #=>  2
proc { |a, b, c| }.arity       #=>  3
proc { |*a| }.arity            #=> -1
proc { |a, *b| }.arity         #=> -2
proc { |a, *b, c| }.arity      #=> -3
proc { |x:, y:, z:0| }.arity   #=>  1
proc { |*a, x:, y:0| }.arity   #=> -2

proc   { |a=0| }.arity         #=>  0
lambda { |a=0| }.arity         #=> -1
proc   { |a=0, b| }.arity      #=>  1
lambda { |a=0, b| }.arity      #=> -2
proc   { |a=0, b=0| }.arity    #=>  0
lambda { |a=0, b=0| }.arity    #=> -1
proc   { |a, b=0| }.arity      #=>  1
lambda { |a, b=0| }.arity      #=> -2
proc   { |(a, b), c=0| }.arity #=>  1
lambda { |(a, b), c=0| }.arity #=> -2
proc   { |a, x:0, y:0| }.arity #=>  1
lambda { |a, x:0, y:0| }.arity #=> -2

Returns:


1066
1067
1068
1069
1070
1071
# File 'proc.c', line 1066

static VALUE
proc_arity(VALUE self)
{
    int arity = rb_proc_arity(self);
    return INT2FIX(arity);
}

#bindingBinding

Returns the binding associated with prc.

def fred(param)
  proc {}
end

b = fred(99)
eval("param", b.binding)   #=> 99

Returns:


3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
# File 'proc.c', line 3281

static VALUE
proc_binding(VALUE self)
{
    VALUE bindval, binding_self = Qundef;
    rb_binding_t *bind;
    const rb_proc_t *proc;
    const rb_iseq_t *iseq = NULL;
    const struct rb_block *block;
    const rb_env_t *env = NULL;

    GetProcPtr(self, proc);
    block = &proc->block;

    if (proc->is_isolated) rb_raise(rb_eArgError, "Can't create Binding from isolated Proc");

  again:
    switch (vm_block_type(block)) {
      case block_type_iseq:
	iseq = block->as.captured.code.iseq;
	binding_self = block->as.captured.self;
	env = VM_ENV_ENVVAL_PTR(block->as.captured.ep);
	break;
      case block_type_proc:
	GetProcPtr(block->as.proc, proc);
	block = &proc->block;
	goto again;
      case block_type_ifunc:
	{
	    const struct vm_ifunc *ifunc = block->as.captured.code.ifunc;
	    if (IS_METHOD_PROC_IFUNC(ifunc)) {
		VALUE method = (VALUE)ifunc->data;
		VALUE name = rb_fstring_lit("<empty_iseq>");
		rb_iseq_t *empty;
		binding_self = method_receiver(method);
		iseq = rb_method_iseq(method);
		env = VM_ENV_ENVVAL_PTR(block->as.captured.ep);
		env = env_clone(env, method_cref(method));
		/* set empty iseq */
		empty = rb_iseq_new(NULL, name, name, Qnil, 0, ISEQ_TYPE_TOP);
		RB_OBJ_WRITE(env, &env->iseq, empty);
		break;
	    }
	}
        /* FALLTHROUGH */
      case block_type_symbol:
        rb_raise(rb_eArgError, "Can't create Binding from C level Proc");
        UNREACHABLE_RETURN(Qnil);
    }

    bindval = rb_binding_alloc(rb_cBinding);
    GetBindingPtr(bindval, bind);
    RB_OBJ_WRITE(bindval, &bind->block.as.captured.self, binding_self);
    RB_OBJ_WRITE(bindval, &bind->block.as.captured.code.iseq, env->iseq);
    rb_vm_block_ep_update(bindval, &bind->block, env->ep);
    RB_OBJ_WRITTEN(bindval, Qundef, VM_ENV_ENVVAL(env->ep));

    if (iseq) {
	rb_iseq_check(iseq);
	RB_OBJ_WRITE(bindval, &bind->pathobj, iseq->body->location.pathobj);
	bind->first_lineno = FIX2INT(rb_iseq_first_lineno(iseq));
    }
    else {
	RB_OBJ_WRITE(bindval, &bind->pathobj,
		     rb_iseq_pathobj_new(rb_fstring_lit("(binding)"), Qnil));
	bind->first_lineno = 1;
    }

    return bindval;
}

#call(*args) ⇒ Object

call-seq:

prc.call(params,...)   -> obj
prc[params,...]        -> obj
prc.(params,...)       -> obj
prc.yield(params,...)  -> obj

Invokes the block, setting the block's parameters to the values in params using something close to method calling semantics. Returns the value of the last expression evaluated in the block.

a_proc = Proc.new {|scalar, *values| values.map {|value| value*scalar } }
a_proc.call(9, 1, 2, 3)    #=> [9, 18, 27]
a_proc[9, 1, 2, 3]         #=> [9, 18, 27]
a_proc.(9, 1, 2, 3)        #=> [9, 18, 27]
a_proc.yield(9, 1, 2, 3)   #=> [9, 18, 27]

Note that prc.() invokes prc.call() with the parameters given. It's syntactic sugar to hide “call”.

For procs created using #lambda or ->() an error is generated if the wrong number of parameters are passed to the proc. For procs created using Proc.new or Kernel.proc, extra parameters are silently discarded and missing parameters are set to nil.

a_proc = proc {|a,b| [a,b] }
a_proc.call(1)   #=> [1, nil]

a_proc = lambda {|a,b| [a,b] }
a_proc.call(1)   # ArgumentError: wrong number of arguments (given 1, expected 2)

See also Proc#lambda?.


944
945
946
947
948
# File 'proc.c', line 944

static VALUE
proc_call(int argc, VALUE *argv, VALUE procval)
{
    /* removed */
}

#cloneObject

:nodoc:


163
164
165
166
167
168
169
# File 'proc.c', line 163

static VALUE
proc_clone(VALUE self)
{
    VALUE procval = rb_proc_dup(self);
    CLONESETUP(procval, self);
    return procval;
}

#curryProc #curry(arity) ⇒ Proc

Returns a curried proc. If the optional arity argument is given, it determines the number of arguments. A curried proc receives some arguments. If a sufficient number of arguments are supplied, it passes the supplied arguments to the original proc and returns the result. Otherwise, returns another curried proc that takes the rest of arguments.

b = proc {|x, y, z| (x||0) + (y||0) + (z||0) }
p b.curry[1][2][3]           #=> 6
p b.curry[1, 2][3, 4]        #=> 6
p b.curry(5)[1][2][3][4][5]  #=> 6
p b.curry(5)[1, 2][3, 4][5]  #=> 6
p b.curry(1)[1]              #=> 1

b = proc {|x, y, z, *w| (x||0) + (y||0) + (z||0) + w.inject(0, &:+) }
p b.curry[1][2][3]           #=> 6
p b.curry[1, 2][3, 4]        #=> 10
p b.curry(5)[1][2][3][4][5]  #=> 15
p b.curry(5)[1, 2][3, 4][5]  #=> 15
p b.curry(1)[1]              #=> 1

b = lambda {|x, y, z| (x||0) + (y||0) + (z||0) }
p b.curry[1][2][3]           #=> 6
p b.curry[1, 2][3, 4]        #=> wrong number of arguments (given 4, expected 3)
p b.curry(5)                 #=> wrong number of arguments (given 5, expected 3)
p b.curry(1)                 #=> wrong number of arguments (given 1, expected 3)

b = lambda {|x, y, z, *w| (x||0) + (y||0) + (z||0) + w.inject(0, &:+) }
p b.curry[1][2][3]           #=> 6
p b.curry[1, 2][3, 4]        #=> 10
p b.curry(5)[1][2][3][4][5]  #=> 15
p b.curry(5)[1, 2][3, 4][5]  #=> 15
p b.curry(1)                 #=> wrong number of arguments (given 1, expected 3)

b = proc { :foo }
p b.curry[]                  #=> :foo

Overloads:


3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
# File 'proc.c', line 3435

static VALUE
proc_curry(int argc, const VALUE *argv, VALUE self)
{
    int sarity, max_arity, min_arity = rb_proc_min_max_arity(self, &max_arity);
    VALUE arity;

    if (rb_check_arity(argc, 0, 1) == 0 || NIL_P(arity = argv[0])) {
	arity = INT2FIX(min_arity);
    }
    else {
	sarity = FIX2INT(arity);
	if (rb_proc_lambda_p(self)) {
	    rb_check_arity(sarity, min_arity, max_arity);
	}
    }

    return make_curry_proc(self, rb_ary_new(), arity);
}

#dupObject


955
956
957
958
959
960
961
962
963
964
965
966
# File 'vm.c', line 955

VALUE
rb_proc_dup(VALUE self)
{
    VALUE procval;
    rb_proc_t *src;

    GetProcPtr(self, src);
    procval = proc_create(rb_cProc, &src->block, src->is_from_method, src->is_lambda);
    if (RB_OBJ_SHAREABLE_P(self)) FL_SET_RAW(procval, RUBY_FL_SHAREABLE);
    RB_GC_GUARD(self); /* for: body = rb_proc_dup(body) */
    return procval;
}

#==(other) ⇒ Boolean #eql?(other) ⇒ Boolean

Two proc are the same if, and only if, they were created from the same code block.

def return_block(&block)
  block
end

def pass_block_twice(&block)
  [return_block(&block), return_block(&block)]
end

block1, block2 = pass_block_twice { puts 'test' }
# Blocks might be instantiated into Proc's lazily, so they may, or may not,
# be the same object.
# But they are produced from the same code block, so they are equal
block1 == block2
#=> true

# Another Proc will never be equal, even if the code is the "same"
block1 == proc { puts 'test' }
#=> false

Overloads:

  • #==(other) ⇒ Boolean

    Returns:

    • (Boolean)
  • #eql?(other) ⇒ Boolean

    Returns:

    • (Boolean)

1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
# File 'proc.c', line 1302

static VALUE
proc_eq(VALUE self, VALUE other)
{
    const rb_proc_t *self_proc, *other_proc;
    const struct rb_block *self_block, *other_block;

    if (rb_obj_class(self) !=  rb_obj_class(other)) {
        return Qfalse;
    }

    GetProcPtr(self, self_proc);
    GetProcPtr(other, other_proc);

    if (self_proc->is_from_method != other_proc->is_from_method ||
            self_proc->is_lambda != other_proc->is_lambda) {
        return Qfalse;
    }

    self_block = &self_proc->block;
    other_block = &other_proc->block;

    if (vm_block_type(self_block) != vm_block_type(other_block)) {
        return Qfalse;
    }

    switch (vm_block_type(self_block)) {
      case block_type_iseq:
        if (self_block->as.captured.ep != \
                other_block->as.captured.ep ||
                self_block->as.captured.code.iseq != \
                other_block->as.captured.code.iseq) {
            return Qfalse;
        }
        break;
      case block_type_ifunc:
        if (self_block->as.captured.ep != \
                other_block->as.captured.ep ||
                self_block->as.captured.code.ifunc != \
                other_block->as.captured.code.ifunc) {
            return Qfalse;
        }
        break;
      case block_type_proc:
        if (self_block->as.proc != other_block->as.proc) {
            return Qfalse;
        }
        break;
      case block_type_symbol:
        if (self_block->as.symbol != other_block->as.symbol) {
            return Qfalse;
        }
        break;
    }

    return Qtrue;
}

#hashInteger

Returns a hash value corresponding to proc body.

See also Object#hash.

Returns:


1480
1481
1482
1483
1484
1485
1486
1487
1488
# File 'proc.c', line 1480

static VALUE
proc_hash(VALUE self)
{
    st_index_t hash;
    hash = rb_hash_start(0);
    hash = rb_hash_proc(hash, self);
    hash = rb_hash_end(hash);
    return ST2FIX(hash);
}

#lambda?Boolean

Returns true if a Proc object is lambda. false if non-lambda.

The lambda-ness affects argument handling and the behavior of return and break.

A Proc object generated by proc ignores extra arguments.

proc {|a,b| [a,b] }.call(1,2,3)    #=> [1,2]

It provides nil for missing arguments.

proc {|a,b| [a,b] }.call(1)        #=> [1,nil]

It expands a single array argument.

proc {|a,b| [a,b] }.call([1,2])    #=> [1,2]

A Proc object generated by lambda doesn't have such tricks.

lambda {|a,b| [a,b] }.call(1,2,3)  #=> ArgumentError
lambda {|a,b| [a,b] }.call(1)      #=> ArgumentError
lambda {|a,b| [a,b] }.call([1,2])  #=> ArgumentError

Proc#lambda? is a predicate for the tricks. It returns true if no tricks apply.

lambda {}.lambda?            #=> true
proc {}.lambda?              #=> false

Proc.new is the same as proc.

Proc.new {}.lambda?          #=> false

lambda, proc and Proc.new preserve the tricks of a Proc object given by & argument.

lambda(&lambda {}).lambda?   #=> true
proc(&lambda {}).lambda?     #=> true
Proc.new(&lambda {}).lambda? #=> true

lambda(&proc {}).lambda?     #=> false
proc(&proc {}).lambda?       #=> false
Proc.new(&proc {}).lambda?   #=> false

A Proc object generated by & argument has the tricks

def n(&b) b.lambda? end
n {}                         #=> false

The & argument preserves the tricks if a Proc object is given by & argument.

n(&lambda {})                #=> true
n(&proc {})                  #=> false
n(&Proc.new {})              #=> false

A Proc object converted from a method has no tricks.

def m() end
method(:m).to_proc.lambda?   #=> true

n(&method(:m))               #=> true
n(&method(:m).to_proc)       #=> true

define_method is treated the same as method definition. The defined method has no tricks.

class C
  define_method(:d) {}
end
C.new.d(1,2)       #=> ArgumentError
C.new.method(:d).to_proc.lambda?   #=> true

define_method always defines a method without the tricks, even if a non-lambda Proc object is given. This is the only exception for which the tricks are not preserved.

class C
  define_method(:e, &proc {})
end
C.new.e(1,2)       #=> ArgumentError
C.new.method(:e).to_proc.lambda?   #=> true

This exception ensures that methods never have tricks and makes it easy to have wrappers to define methods that behave as usual.

class C
  def self.def2(name, &body)
    define_method(name, &body)
  end

  def2(:f) {}
end
C.new.f(1,2)       #=> ArgumentError

The wrapper def2 defines a method which has no tricks.

Returns:

  • (Boolean)

274
275
276
277
278
279
280
281
# File 'proc.c', line 274

VALUE
rb_proc_lambda_p(VALUE procval)
{
    rb_proc_t *proc;
    GetProcPtr(procval, proc);

    return proc->is_lambda ? Qtrue : Qfalse;
}

#parametersArray

Returns the parameter information of this proc.

prc = lambda{|x, y=42, *other|}
prc.parameters  #=> [[:req, :x], [:opt, :y], [:rest, :other]]

Returns:


1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
# File 'proc.c', line 1421

static VALUE
rb_proc_parameters(VALUE self)
{
    int is_proc;
    const rb_iseq_t *iseq = rb_proc_get_iseq(self, &is_proc);
    if (!iseq) {
	return rb_unnamed_parameters(rb_proc_arity(self));
    }
    return rb_iseq_parameters(iseq, is_proc);
}

#ruby2_keywordsProc

Marks the proc as passing keywords through a normal argument splat. This should only be called on procs that accept an argument splat (*args) but not explicit keywords or a keyword splat. It marks the proc such that if the proc is called with keyword arguments, the final hash argument is marked with a special flag such that if it is the final element of a normal argument splat to another method call, and that method call does not include explicit keywords or a keyword splat, the final element is interpreted as keywords. In other words, keywords will be passed through the proc to other methods.

This should only be used for procs that delegate keywords to another method, and only for backwards compatibility with Ruby versions before 2.7.

This method will probably be removed at some point, as it exists only for backwards compatibility. As it does not exist in Ruby versions before 2.7, check that the proc responds to this method before calling it. Also, be aware that if this method is removed, the behavior of the proc will change so that it does not pass through keywords.

module Mod
  foo = ->(meth, *args, &block) do
    send(:"do_#{meth}", *args, &block)
  end
  foo.ruby2_keywords if foo.respond_to?(:ruby2_keywords)
end

Returns:


3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
# File 'proc.c', line 3706

static VALUE
proc_ruby2_keywords(VALUE procval)
{
    rb_proc_t *proc;
    GetProcPtr(procval, proc);

    rb_check_frozen(procval);

    if (proc->is_from_method) {
            rb_warn("Skipping set of ruby2_keywords flag for proc (proc created from method)");
            return procval;
    }

    switch (proc->block.type) {
      case block_type_iseq:
        if (proc->block.as.captured.code.iseq->body->param.flags.has_rest &&
                !proc->block.as.captured.code.iseq->body->param.flags.has_kw &&
                !proc->block.as.captured.code.iseq->body->param.flags.has_kwrest) {
            proc->block.as.captured.code.iseq->body->param.flags.ruby2_keywords = 1;
        }
        else {
            rb_warn("Skipping set of ruby2_keywords flag for proc (proc accepts keywords or proc does not accept argument splat)");
        }
        break;
      default:
        rb_warn("Skipping set of ruby2_keywords flag for proc (proc not defined in Ruby)");
        break;
    }

    return procval;
}

#source_locationArray, Integer

Returns the Ruby source filename and line number containing this proc or nil if this proc was not defined in Ruby (i.e. native).

Returns ].

Returns:


1386
1387
1388
1389
1390
# File 'proc.c', line 1386

VALUE
rb_proc_location(VALUE self)
{
    return iseq_location(rb_proc_get_iseq(self, 0));
}

#to_procProc

Part of the protocol for converting objects to Proc objects. Instances of class Proc simply return themselves.

Returns:


1546
1547
1548
1549
1550
# File 'proc.c', line 1546

static VALUE
proc_to_proc(VALUE self)
{
    return self;
}

#to_sString Also known as: inspect

Returns the unique identifier for this proc, along with an indication of where the proc was defined.

Returns:


1530
1531
1532
1533
1534
1535
1536
# File 'proc.c', line 1530

static VALUE
proc_to_s(VALUE self)
{
    const rb_proc_t *proc;
    GetProcPtr(self, proc);
    return rb_block_to_s(self, &proc->block, proc->is_lambda ? " (lambda)" : NULL);
}

#yield(*args) ⇒ Object

call-seq:

prc.call(params,...)   -> obj
prc[params,...]        -> obj
prc.(params,...)       -> obj
prc.yield(params,...)  -> obj

Invokes the block, setting the block's parameters to the values in params using something close to method calling semantics. Returns the value of the last expression evaluated in the block.

a_proc = Proc.new {|scalar, *values| values.map {|value| value*scalar } }
a_proc.call(9, 1, 2, 3)    #=> [9, 18, 27]
a_proc[9, 1, 2, 3]         #=> [9, 18, 27]
a_proc.(9, 1, 2, 3)        #=> [9, 18, 27]
a_proc.yield(9, 1, 2, 3)   #=> [9, 18, 27]

Note that prc.() invokes prc.call() with the parameters given. It's syntactic sugar to hide “call”.

For procs created using #lambda or ->() an error is generated if the wrong number of parameters are passed to the proc. For procs created using Proc.new or Kernel.proc, extra parameters are silently discarded and missing parameters are set to nil.

a_proc = proc {|a,b| [a,b] }
a_proc.call(1)   #=> [1, nil]

a_proc = lambda {|a,b| [a,b] }
a_proc.call(1)   # ArgumentError: wrong number of arguments (given 1, expected 2)

See also Proc#lambda?.


944
945
946
947
948
# File 'proc.c', line 944

static VALUE
proc_call(int argc, VALUE *argv, VALUE procval)
{
    /* removed */
}