# class Method

`Method` objects are created by `Object#method`, and are associated with a particular object (not just with a class). They may be used to invoke the method within the object, and as a block associated with an iterator. They may also be unbound from one object (creating an `UnboundMethod`) and bound to another.

    class Thing
      def square(n)
        n*n
      end
    end
    thing = Thing.new
    meth  = thing.method(:square)

    meth.call(9)                 #=> 81
    [ 1, 2, 3 ].collect(&meth)   #=> [1, 4, 9]

    [ 1, 2, 3 ].each(&method(:puts)) #=> prints 1, 2, 3

    require 'date'
    %w[2017-03-01 2017-03-02].collect(&Date.method(:parse))
    #=> [#<Date: 2017-03-01 ((2457814j,0s,0n),+0s,2299161j)>, #<Date: 2017-03-02 ((2457815j,0s,0n),+0s,2299161j)>]

### Public Instance Methods

meth << g → a_proc click to toggle source

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

    def f(x)
      x * x
    end

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

    static VALUE
    rb_method_compose_to_left(VALUE self, VALUE g)
    {
        VALUE proc = method_to_proc(self);
        return proc_compose_to_left(proc, g);
    }

meth == other_meth → true or false click to toggle source

Two method objects are equal if they are bound to the same object and refer to the same method definition and their owners are the same class or module.

    static VALUE
    method_eq(VALUE method, VALUE other)
    {
        struct METHOD *m1, *m2;
        VALUE klass1, klass2;

        if (!rb_obj_is_method(other))
            return Qfalse;
        if (CLASS_OF(method) != CLASS_OF(other))
            return Qfalse;

        Check_TypedStruct(method, &method_data_type);
        m1 = (struct METHOD *)DATA_PTR(method);
        m2 = (struct METHOD *)DATA_PTR(other);

        klass1 = method_entry_defined_class(m1->me);
        klass2 = method_entry_defined_class(m2->me);

        if (!rb_method_entry_eq(m1->me, m2->me) ||
            klass1 != klass2 ||
            m1->klass != m2->klass ||
            m1->recv != m2->recv) {
            return Qfalse;
        }

        return Qtrue;
    }

method === obj → result_of_method click to toggle source

Invokes the method with `obj` as the parameter like `call`. This allows a method object to be the target of a `when` clause in a case statement.

    require 'prime'

    case 1373
    when Prime.method(:prime?)
      # ...
    end

    VALUE
    rb_method_call(int argc, const VALUE *argv, VALUE method)
    {
        VALUE procval = rb_block_given_p() ? rb_block_proc() : Qnil;
        return rb_method_call_with_block(argc, argv, method, procval);
    }

meth >> g → a_proc click to toggle source

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

    def f(x)
      x * x
    end

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

    static VALUE
    rb_method_compose_to_right(VALUE self, VALUE g)
    {
        VALUE proc = method_to_proc(self);
        return proc_compose_to_right(proc, g);
    }

meth[args, ...] → obj click to toggle source

Invokes the meth with the specified arguments, returning the method's return value.

    m = 12.method("+")
    m.call(3)    #=> 15
    m.call(20)   #=> 32

    VALUE
    rb_method_call(int argc, const VALUE *argv, VALUE method)
    {
        VALUE procval = rb_block_given_p() ? rb_block_proc() : Qnil;
        return rb_method_call_with_block(argc, argv, method, procval);
    }

arity → integer click to toggle source

Returns an indication of the number of arguments accepted by a method. Returns a nonnegative integer for methods that take a fixed number of arguments. For Ruby methods that take a variable number of arguments, returns -n-1, where n is the number of required arguments. Keyword arguments will be considered as a single additional argument, that argument being mandatory if any keyword argument is mandatory. For methods written in C, returns -1 if the call takes a variable number of arguments.

    class C
      def one;    end
      def two(a); end
      def three(*a);  end
      def four(a, b); end
      def five(a, b, *c);    end
      def six(a, b, *c, &d); end
      def seven(a, b, x:0); end
      def eight(x:, y:); end
      def nine(x:, y:, **z); end
      def ten(*a, x:, y:); end
    end
    c = C.new
    c.method(:one).arity     #=> 0
    c.method(:two).arity     #=> 1
    c.method(:three).arity   #=> -1
    c.method(:four).arity    #=> 2
    c.method(:five).arity    #=> -3
    c.method(:six).arity     #=> -3
    c.method(:seven).arity   #=> -3
    c.method(:eight).arity   #=> 1
    c.method(:nine).arity    #=> 1
    c.method(:ten).arity     #=> -2

    "cat".method(:size).arity      #=> 0
    "cat".method(:replace).arity   #=> 1
    "cat".method(:squeeze).arity   #=> -1
    "cat".method(:count).arity     #=> -1

    static VALUE
    method_arity_m(VALUE method)
    {
        int n = method_arity(method);
        return INT2FIX(n);
    }

call(args, ...) → obj click to toggle source

Invokes the meth with the specified arguments, returning the method's return value.

    m = 12.method("+")
    m.call(3)    #=> 15
    m.call(20)   #=> 32

    VALUE
    rb_method_call(int argc, const VALUE *argv, VALUE method)
    {
        VALUE procval = rb_block_given_p() ? rb_block_proc() : Qnil;
        return rb_method_call_with_block(argc, argv, method, procval);
    }

clone → new_method click to toggle source

Returns a clone of this method.

    class A
      def foo
        return "bar"
      end
    end

    m = A.new.method(:foo)
    m.call # => "bar"
    n = m.clone.call # => "bar"

    static VALUE
    method_clone(VALUE self)
    {
        VALUE clone;
        struct METHOD *orig, *data;

        TypedData_Get_Struct(self, struct METHOD, &method_data_type, orig);
        clone = TypedData_Make_Struct(CLASS_OF(self), struct METHOD, &method_data_type, data);
        CLONESETUP(clone, self);
        RB_OBJ_WRITE(clone, &data->recv, orig->recv);
        RB_OBJ_WRITE(clone, &data->klass, orig->klass);
        RB_OBJ_WRITE(clone, &data->me, rb_method_entry_clone(orig->me));
        return clone;
    }

curry → proc click to toggle source
curry(arity) → proc

Returns a curried proc based on the method. When the proc is called with a number of arguments that is lower than the method's arity, then another curried proc is returned. Only when enough arguments have been supplied to satisfy the method signature, will the method actually be called.

The optional arity argument should be supplied when currying methods with variable arguments to determine how many arguments are needed before the method is called.

    def foo(a,b,c)
      [a, b, c]
    end

    proc  = self.method(:foo).curry
    proc2 = proc.call(1, 2)          #=> #<Proc>
    proc2.call(3)                    #=> [1,2,3]

    def vararg(*args)
      args
    end

    proc = self.method(:vararg).curry(4)
    proc2 = proc.call(:x)      #=> #<Proc>
    proc3 = proc2.call(:y, :z) #=> #<Proc>
    proc3.call(:a)             #=> [:x, :y, :z, :a]

    static VALUE
    rb_method_curry(int argc, const VALUE *argv, VALUE self)
    {
        VALUE proc = method_to_proc(self);
        return proc_curry(argc, argv, proc);
    }

eql?(other_meth) → true or false click to toggle source

Two method objects are equal if they are bound to the same object and refer to the same method definition and their owners are the same class or module.

    static VALUE
    method_eq(VALUE method, VALUE other)
    {
        struct METHOD *m1, *m2;
        VALUE klass1, klass2;

        if (!rb_obj_is_method(other))
            return Qfalse;
        if (CLASS_OF(method) != CLASS_OF(other))
            return Qfalse;

        Check_TypedStruct(method, &method_data_type);
        m1 = (struct METHOD *)DATA_PTR(method);
        m2 = (struct METHOD *)DATA_PTR(other);

        klass1 = method_entry_defined_class(m1->me);
        klass2 = method_entry_defined_class(m2->me);

        if (!rb_method_entry_eq(m1->me, m2->me) ||
            klass1 != klass2 ||
            m1->klass != m2->klass ||
            m1->recv != m2->recv) {
            return Qfalse;
        }

        return Qtrue;
    }

hash → integer click to toggle source

Returns a hash value corresponding to the method object.

See also Object#hash.

    static VALUE
    method_hash(VALUE method)
    {
        struct METHOD *m;
        st_index_t hash;

        TypedData_Get_Struct(method, struct METHOD, &method_data_type, m);
        hash = rb_hash_start((st_index_t)m->recv);
        hash = rb_hash_method_entry(hash, m->me);
        hash = rb_hash_end(hash);

        return ST2FIX(hash);
    }

inspect → string click to toggle source

Returns a human-readable description of the underlying method.

    "cat".method(:count).inspect   #=> "#<Method: String#count>"
    (1..3).method(:map).inspect    #=> "#<Method: Range(Enumerable)#map>"

In the latter case, the method description includes the “owner” of the original method (`Enumerable` module, which is included into `Range`).

    static VALUE
    method_inspect(VALUE method)
    {
        struct METHOD *data;
        VALUE str;
        const char *sharp = "#";
        VALUE mklass;
        VALUE defined_class;

        TypedData_Get_Struct(method, struct METHOD, &method_data_type, data);
        str = rb_sprintf("#<% "PRIsVALUE": ", rb_obj_class(method));
        OBJ_INFECT_RAW(str, method);

        mklass = data->klass;

        if (data->me->def->type == VM_METHOD_TYPE_ALIAS) {
            defined_class = data->me->def->body.alias.original_me->owner;
        }
        else {
            defined_class = method_entry_defined_class(data->me);
        }

        if (RB_TYPE_P(defined_class, T_ICLASS)) {
            defined_class = RBASIC_CLASS(defined_class);
        }

        if (FL_TEST(mklass, FL_SINGLETON)) {
            VALUE v = rb_ivar_get(mklass, attached);

            if (data->recv == Qundef) {
                rb_str_buf_append(str, rb_inspect(mklass));
            }
            else if (data->recv == v) {
                rb_str_buf_append(str, rb_inspect(v));
                sharp = ".";
            }
            else {
                rb_str_buf_append(str, rb_inspect(data->recv));
                rb_str_buf_cat2(str, "(");
                rb_str_buf_append(str, rb_inspect(v));
                rb_str_buf_cat2(str, ")");
                sharp = ".";
            }
        }
        else {
            rb_str_buf_append(str, rb_inspect(mklass));
            if (defined_class != mklass) {
                rb_str_catf(str, "(% "PRIsVALUE")", defined_class);
            }
        }
        rb_str_buf_cat2(str, sharp);
        rb_str_append(str, rb_id2str(data->me->called_id));
        if (data->me->called_id != data->me->def->original_id) {
            rb_str_catf(str, "(%"PRIsVALUE")",
                        rb_id2str(data->me->def->original_id));
        }
        if (data->me->def->type == VM_METHOD_TYPE_NOTIMPLEMENTED) {
            rb_str_buf_cat2(str, " (not-implemented)");
        }
        rb_str_buf_cat2(str, ">");

        return str;
    }

name → symbol click to toggle source

Returns the name of the method.

    static VALUE
    method_name(VALUE obj)
    {
        struct METHOD *data;

        TypedData_Get_Struct(obj, struct METHOD, &method_data_type, data);
        return ID2SYM(data->me->called_id);
    }

original_name → symbol click to toggle source

Returns the original name of the method.

    class C
      def foo; end
      alias bar foo
    end
    C.instance_method(:bar).original_name # => :foo

    static VALUE
    method_original_name(VALUE obj)
    {
        struct METHOD *data;

        TypedData_Get_Struct(obj, struct METHOD, &method_data_type, data);
        return ID2SYM(data->me->def->original_id);
    }

owner → class_or_module click to toggle source

Returns the class or module that defines the method. See also receiver.

    (1..3).method(:map).owner #=> Enumerable

    static VALUE
    method_owner(VALUE obj)
    {
        struct METHOD *data;
        TypedData_Get_Struct(obj, struct METHOD, &method_data_type, data);
        return data->me->owner;
    }

parameters → array click to toggle source

Returns the parameter information of this method.

    def foo(bar); end
    method(:foo).parameters #=> [[:req, :bar]]

    def foo(bar, baz, bat, &blk); end
    method(:foo).parameters #=> [[:req, :bar], [:req, :baz], [:req, :bat], [:block, :blk]]

    def foo(bar, *args); end
    method(:foo).parameters #=> [[:req, :bar], [:rest, :args]]

    def foo(bar, baz, *args, &blk); end
    method(:foo).parameters #=> [[:req, :bar], [:req, :baz], [:rest, :args], [:block, :blk]]

    static VALUE
    rb_method_parameters(VALUE method)
    {
        const rb_iseq_t *iseq = rb_method_iseq(method);
        if (!iseq) {
            return rb_unnamed_parameters(method_arity(method));
        }
        return rb_iseq_parameters(iseq, 0);
    }

receiver → object click to toggle source

Returns the bound receiver of the method object.

    (1..3).method(:map).receiver # => 1..3

    static VALUE
    method_receiver(VALUE obj)
    {
        struct METHOD *data;

        TypedData_Get_Struct(obj, struct METHOD, &method_data_type, data);
        return data->recv;
    }

source_location → [String, Integer] click to toggle source

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

    VALUE
    rb_method_location(VALUE method)
    {
        return method_def_location(rb_method_def(method));
    }

super_method → method click to toggle source

Returns a `Method` of superclass which would be called when super is used or nil if there is no method on superclass.

    static VALUE
    method_super_method(VALUE method)
    {
        const struct METHOD *data;
        VALUE super_class, iclass;
        ID mid;
        const rb_method_entry_t *me;

        TypedData_Get_Struct(method, struct METHOD, &method_data_type, data);
        iclass = data->iclass;
        if (!iclass) return Qnil;
        super_class = RCLASS_SUPER(RCLASS_ORIGIN(iclass));
        mid = data->me->called_id;
        if (!super_class) return Qnil;
        me = (rb_method_entry_t *)rb_callable_method_entry_without_refinements(super_class, mid, &iclass);
        if (!me) return Qnil;
        return mnew_internal(me, me->owner, iclass, data->recv, mid, rb_obj_class(method), FALSE, FALSE);
    }

to_proc → proc click to toggle source

Returns a `Proc` object corresponding to this method.

    static VALUE
    method_to_proc(VALUE method)
    {
        VALUE procval;
        rb_proc_t *proc;

        /*
         * class Method
         *   def to_proc
         *     lambda{|*args|
         *       self.call(*args)
         *     }
         *   end
         * end
         */
        procval = rb_iterate(mlambda, 0, bmcall, method);
        GetProcPtr(procval, proc);
        proc->is_from_method = 1;
        return procval;
    }

to_s → string click to toggle source

Returns a human-readable description of the underlying method.

    "cat".method(:count).inspect   #=> "#<Method: String#count>"
    (1..3).method(:map).inspect    #=> "#<Method: Range(Enumerable)#map>"

In the latter case, the method description includes the “owner” of the original method (`Enumerable` module, which is included into `Range`).

    static VALUE
    method_inspect(VALUE method)
    {
        struct METHOD *data;
        VALUE str;
        const char *sharp = "#";
        VALUE mklass;
        VALUE defined_class;

        TypedData_Get_Struct(method, struct METHOD, &method_data_type, data);
        str = rb_sprintf("#<% "PRIsVALUE": ", rb_obj_class(method));
        OBJ_INFECT_RAW(str, method);

        mklass = data->klass;

        if (data->me->def->type == VM_METHOD_TYPE_ALIAS) {
            defined_class = data->me->def->body.alias.original_me->owner;
        }
        else {
            defined_class = method_entry_defined_class(data->me);
        }

        if (RB_TYPE_P(defined_class, T_ICLASS)) {
            defined_class = RBASIC_CLASS(defined_class);
        }

        if (FL_TEST(mklass, FL_SINGLETON)) {
            VALUE v = rb_ivar_get(mklass, attached);

            if (data->recv == Qundef) {
                rb_str_buf_append(str, rb_inspect(mklass));
            }
            else if (data->recv == v) {
                rb_str_buf_append(str, rb_inspect(v));
                sharp = ".";
            }
            else {
                rb_str_buf_append(str, rb_inspect(data->recv));
                rb_str_buf_cat2(str, "(");
                rb_str_buf_append(str, rb_inspect(v));
                rb_str_buf_cat2(str, ")");
                sharp = ".";
            }
        }
        else {
            rb_str_buf_append(str, rb_inspect(mklass));
            if (defined_class != mklass) {
                rb_str_catf(str, "(% "PRIsVALUE")", defined_class);
            }
        }
        rb_str_buf_cat2(str, sharp);
        rb_str_append(str, rb_id2str(data->me->called_id));
        if (data->me->called_id != data->me->def->original_id) {
            rb_str_catf(str, "(%"PRIsVALUE")",
                        rb_id2str(data->me->def->original_id));
        }
        if (data->me->def->type == VM_METHOD_TYPE_NOTIMPLEMENTED) {
            rb_str_buf_cat2(str, " (not-implemented)");
        }
        rb_str_buf_cat2(str, ">");

        return str;
    }

unbind → unbound_method click to toggle source

Dissociates meth from its current receiver. The resulting `UnboundMethod` can subsequently be bound to a new object of the same class (see `UnboundMethod`).

    static VALUE
    method_unbind(VALUE obj)
    {
        VALUE method;
        struct METHOD *orig, *data;

        TypedData_Get_Struct(obj, struct METHOD, &method_data_type, orig);
        method = TypedData_Make_Struct(rb_cUnboundMethod, struct METHOD,
                                       &method_data_type, data);
        RB_OBJ_WRITE(method, &data->recv, Qundef);
        RB_OBJ_WRITE(method, &data->klass, orig->klass);
        RB_OBJ_WRITE(method, &data->me, rb_method_entry_clone(orig->me));
        OBJ_INFECT(method, obj);

        return method;
    }