Class: Binding

Inherits:
Object show all
Defined in:
proc.c

Overview

Objects of class Binding encapsulate the execution context at some particular place in the code and retain this context for future use. The variables, methods, value of self, and possibly an iterator block that can be accessed in this context are all retained. Binding objects can be created using Kernel#binding, and are made available to the callback of Kernel#set_trace_func.

These binding objects can be passed as the second argument of the Kernel#eval method, establishing an environment for the evaluation.

class Demo
  def initialize(n)
    @secret = n
  end
  def get_binding
    return binding()
  end
end

k1 = Demo.new(99)
b1 = k1.get_binding
k2 = Demo.new(-3)
b2 = k2.get_binding

eval("@secret", b1)   #=> 99
eval("@secret", b2)   #=> -3
eval("@secret")       #=> nil

Binding objects have no class-specific methods.

Instance Method Summary collapse

Instance Method Details

#clone ⇒ Object

:nodoc:



311
312
313
314
315
316
317
 
# File 'proc.c', line 311

static VALUE
binding_clone(VALUE self)
{
    VALUE bindval = binding_dup(self);
    CLONESETUP(bindval, self);
    return bindval;
}

#dup ⇒ Object

:nodoc:



296
297
298
299
300
301
302
303
304
305
306
307
308
 
# File 'proc.c', line 296

static VALUE
binding_dup(VALUE self)
{
    VALUE bindval = rb_binding_alloc(rb_cBinding);
    rb_binding_t *src, *dst;
    GetBindingPtr(self, src);
    GetBindingPtr(bindval, dst);
    dst->env = src->env;
    dst->path = src->path;
    dst->blockprocval = src->blockprocval;
    dst->first_lineno = src->first_lineno;
    return bindval;
}

#eval(string[, filename [,lineno]]) ⇒ Object

Evaluates the Ruby expression(s) in string, in the binding’s context. If the optional filename and lineno parameters are present, they will be used when reporting syntax errors.

def get_binding(param)
  return binding
end
b = get_binding("hello")
b.eval("param")   #=> "hello"

Returns:



370
371
372
373
374
375
376
377
378
 
# File 'proc.c', line 370

static VALUE
bind_eval(int argc, VALUE *argv, VALUE bindval)
{
    VALUE args[4];

    rb_scan_args(argc, argv, "12", &args[0], &args[2], &args[3]);
    args[1] = bindval;
    return rb_f_eval(argc+1, args, Qnil /* self will be searched in eval */);
}

#local_variable_defined?(symbol) ⇒ Object

Returns a true if a local variable symbol exists.

def foo a = 1 binding.local_variable_defined?(:a) #=> true binding.local_variable_defined?(:b) #=> false end

This method is short version of the following code.

binding.eval(“defined?(#symbol) == ‘local-variable’”)

Returns:

Returns:

  • (Boolean) 


526
527
528
529
530
531
532
533
534
535
536
 
# File 'proc.c', line 526

static VALUE
bind_local_variable_defined_p(VALUE bindval, VALUE sym)
{
    ID lid = check_local_id(bindval, &sym);
    const rb_binding_t *bind;

    if (!lid) return Qfalse;

    GetBindingPtr(bindval, bind);
    return get_local_variable_ptr(bind->env, lid) ? Qtrue : Qfalse;
}

#local_variable_get(symbol) ⇒ Object

Returns a value of local variable symbol.

def foo a = 1 binding.local_variable_get(:a) #=> 1 binding.local_variable_get(:b) #=> NameError end

This method is short version of the following code.

binding.eval(“#symbol”)

Returns:



445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
 
# File 'proc.c', line 445

static VALUE
bind_local_variable_get(VALUE bindval, VALUE sym)
{
    ID lid = check_local_id(bindval, &sym);
    const rb_binding_t *bind;
    const VALUE *ptr;

    if (!lid) goto undefined;

    GetBindingPtr(bindval, bind);

    if ((ptr = get_local_variable_ptr(bind->env, lid)) == NULL) {
      undefined:
	rb_name_error_str(sym, "local variable `%"PRIsVALUE"' not defined for %"PRIsVALUE,
			  sym, bindval);
    }

    return *ptr;
}

#local_variable_set(symbol, obj) ⇒ Object

Set local variable named symbol as obj.

def foo a = 1 b = binding b.local_variable_set(:a, 2) # set existing local variable ‘a’ b.local_variable_set(:b, 3) # create new local variable ‘b’ # ‘b’ exists only in binding. b.local_variable_get(:a) #=> 2 b.local_variable_get(:b) #=> 3 p a #=> 2 p b #=> NameError end

This method is a similar behavior of the following code

binding.eval("#{symbol} = #{obj}")

if obj can be dumped in Ruby code.

Returns:



489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
 
# File 'proc.c', line 489

static VALUE
bind_local_variable_set(VALUE bindval, VALUE sym, VALUE val)
{
    ID lid = check_local_id(bindval, &sym);
    rb_binding_t *bind;
    VALUE *ptr;

    if (!lid) lid = rb_intern_str(sym);

    GetBindingPtr(bindval, bind);
    if ((ptr = get_local_variable_ptr(bind->env, lid)) == NULL) {
	/* not found. create new env */
	ptr = rb_binding_add_dynavars(bind, 1, &lid);
    }

    *ptr = val;

    return val;
}