# class Binding

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
        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.

### Public Instance Methods

eval(string [, filename [,lineno]]) → obj click to toggle source

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

    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) → obj click to toggle source

Returns `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 the short version of the following code:

    binding.eval("defined?(#{symbol}) == 'local-variable'")

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

        if (!lid) return Qfalse;

        GetBindingPtr(bindval, bind);
        env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
        return get_local_variable_ptr(&env, lid) ? Qtrue : Qfalse;
    }

local_variable_get(symbol) → obj click to toggle source

Returns the value of the local variable `symbol`.

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

This method is the short version of the following code:

    binding.eval("#{symbol}")

    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;
        const rb_env_t *env;

        if (!lid) goto undefined;

        GetBindingPtr(bindval, bind);

        env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
        if ((ptr = get_local_variable_ptr(&env, lid)) == NULL) {
            sym = ID2SYM(lid);
          undefined:
            rb_name_err_raise("local variable `%1$s' is not defined for %2$s",
                              bindval, sym);
        }

        return *ptr;
    }

local_variable_set(symbol, obj) → obj click to toggle source

Set local variable named `symbol` as `obj`.

    def foo
      a = 1
      bind = binding
      bind.local_variable_set(:a, 2) # set existing local variable `a'
      bind.local_variable_set(:b, 3) # create new local variable `b'
                                     # `b' exists only in binding

      p bind.local_variable_get(:a)  #=> 2
      p bind.local_variable_get(:b)  #=> 3
      p a                            #=> 2
      p b                            #=> NameError
    end

This method behaves similarly to the following code:

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

if `obj` can be dumped in Ruby code.

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

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

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

        RB_OBJ_WRITE(env, ptr, val);

        return val;
    }

local_variables → Array click to toggle source

Returns the names of the binding's local variables as symbols.

    def foo
      a = 1
      2.times do |n|
        binding.local_variables #=> [:a, :n]
      end
    end

This method is the short version of the following code:

    binding.eval("local_variables")

    static VALUE
    bind_local_variables(VALUE bindval)
    {
        const rb_binding_t *bind;
        const rb_env_t *env;

        GetBindingPtr(bindval, bind);
        env = VM_ENV_ENVVAL_PTR(vm_block_ep(&bind->block));
        return rb_vm_env_local_variables(env);
    }

receiver → object click to toggle source

Returns the bound receiver of the binding object.

    static VALUE
    bind_receiver(VALUE bindval)
    {
        const rb_binding_t *bind;
        GetBindingPtr(bindval, bind);
        return vm_block_self(&bind->block);
    }