Feature #5007

Proc#call_under: Unifying instance_eval and instance_exec

Added by judofyr (Magnus Holm) about 6 years ago. Updated about 4 years ago.

Target version:


I'm proposing a method called Proc#call_under (the name could be
discussed) which both unifies instance_eval and instance_exec, and makes
it possible to call a Proc with a block and a scope:

Proc#call_under(self, *args, &blk):

proc { self }.call_under(1) # => 1

proc { |a| self + a }.call_under(1, 2) # => 3

proc { |&b| self + }.call_under(2) { 2 } # => 4
proc_call_under.patch (2.06 KB) proc_call_under.patch mame (Yusuke Endoh), 04/17/2012 10:52 PM

Related issues

Related to Ruby trunk - Feature #6298: Proc#+Rejected2012-04-15


#1 [ruby-core:43650] Updated by mame (Yusuke Endoh) over 5 years ago

  • Assignee set to matz (Yukihiro Matsumoto)
  • Status changed from Open to Assigned

#2 [ruby-core:44394] Updated by trans (Thomas Sawyer) over 5 years ago

I don't see how this solves the case presented in #6298.


class BlockCollection
def initialize(*procs)
@procs = procs
def to_proc
procs = @procs{ |*a| procs.each{ |p| p.call_under(self, *a) } }

What is self here, or what should it be? Such that:

module M
A ={ self }

bc = #=> M

'F'.instance_eval(&bc) #=> 'F'


#3 [ruby-core:44422] Updated by mame (Yusuke Endoh) over 5 years ago


I made a proof-of-concept patch.
Not tested yet. Please try it and find a bug.
It (and some related functions) seem to need some refactoring work
because it calls directly invoke_block_from_c which is very internal

$ ./miniruby -e '
p proc { self }.call_under(1)
p proc { |a| self + a }.call_under(1, 2)
p proc { |&b| self + }.call_under(2) { 2 }

diff --git a/proc.c b/proc.c
index d44e8d8..7ad490e 100644
--- a/proc.c
+++ b/proc.c
@@ -567,6 +567,22 @@ proc_call(int argc, VALUE *argv, VALUE procval)
return vret;

+VALUE rb_proc_call_under(VALUE procval, VALUE under, VALUE self, VALUE values);
+static VALUE
+proc_call_under(int argc, VALUE argv, VALUE procval)
+ VALUE self, klass, values;
+ rb_scan_args(argc, argv, "1
", &self, &values);
+ if (SPECIAL_CONST_P(self)) {
+ klass = Qnil;
+ }
+ else {
+ klass = rb_singleton_class(self);
+ }
+ return rb_proc_call_under(procval, klass, self, values);
static inline int
check_argc(long argc)
@@ -2183,6 +2199,7 @@ Init_Proc(void)
rb_define_method(rb_cProc, "[]", proc_call, -1);
rb_define_method(rb_cProc, "===", proc_call, -1);
rb_define_method(rb_cProc, "yield", proc_call, -1);
+ rb_define_method(rb_cProc, "call_under", proc_call_under, -1);
rb_define_method(rb_cProc, "to_proc", proc_to_proc, 0);
rb_define_method(rb_cProc, "arity", proc_arity, 0);
diff --git a/vm_eval.c b/vm_eval.c
index 6c26b97..562a215 100644
--- a/vm_eval.c
+++ b/vm_eval.c
@@ -1262,6 +1262,30 @@ yield_under(VALUE under, VALUE self, VALUE values)

+static inline VALUE
+invoke_block_from_c(rb_thread_t th, const rb_block_t *block,
+ VALUE self, int argc, const VALUE *argv,
+ const rb_block_t *blockptr, const NODE *cref);
+rb_proc_call_under(VALUE procval, VALUE under, VALUE self, VALUE values)
+ rb_thread_t *th = GET_THREAD();
+ rb_block_t block;
+ NODE *cref;
+ rb_proc_t *proc;
+ GetProcPtr(procval, proc);
+ block = proc->block;
+ block.self = self;
+ cref = vm_cref_push(th, under, NOEX_PUBLIC, &proc->block);
+ cref->flags |= NODE_FL_CREF_PUSHED_BY_EVAL;
+ return invoke_block_from_c(th, &block, self,
+ RARRAY_LENINT(values), RARRAY_PTR(values),
+ GC_GUARDED_PTR_REF(th->cfp->lfp[0]), cref);
string eval under the class/module context */
static VALUE
eval_under(VALUE under, VALUE self, VALUE src, const char *file, int line)

Yusuke Endoh

#4 Updated by mame (Yusuke Endoh) over 4 years ago

  • Target version set to next minor

#5 [ruby-core:55692] Updated by judofyr (Magnus Holm) about 4 years ago

I concur with trans: I don't think this issue will solve #6298. However, please keep that discussion out of this issue.

Would it be possible to get a OK/NG for inclusion of this in 2.1?

Still not sure about the name. Maybe #call_with is better?

#6 [ruby-core:55694] Updated by phluid61 (Matthew Kerwin) about 4 years ago

judofyr (Magnus Holm) wrote:

Still not sure about the name. Maybe #call_with is better?

I suggest #call_as or #call_bound: "as" because it suggests that "self" in the proc will refer to the first parameter, or possibly "bound" because we're binding the proc to the object (as well as to its existing binding scope). However I don't have strong feelings about any name, except that I like #call_with less than any others.

A side discussion: how does this tie in with currying? For example, do you foresee a Proc#curry_under (or curry_self, or curry_with, or whatever) method, that would cause the proc to be passed to instance_exec when all its parameters are satisfied?

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