• Mek101 (11/19) Jun 12 2019 Say that I may want to use the function in a @nogc scope,
• H. S. Teoh (26/40) Jun 12 2019 [...]
• Mek101 (2/2) Jun 12 2019 I didn't know it applied to templates other than lambdas.
• Jacob Carlborg (5/8) Jun 13 2019 It applies to templates, lambdas (which basically are templates) and
• Jonathan M Davis (5/11) Jun 13 2019 It also now applies to auto return functions, though that's a more recen...

Mek101 <anEmailAddress mail.somewhere> writes:

I'll try to be straight.

I have the following function:

public size_t indexOf(alias pred = "a == b", Range)(Range array)
{
	alias predicate = unaryFun!pred;
	for(size_t i = 0; i < array.length; i++)
		if(predicate(array[i]))
			return i;
	return size_t.max;
}

Say that I may want to use the function in a  nogc scope, 
providing a  nogc callable, but I also want to reuse the same 
code in managed scope while passing a delegate: how can I apply 
the attributes of the given callable to the function so that 
they're automatically determined at compile time?

I know of std.traits.SetFunctionAttributes and 
std.traits.FunctionAttributes, but I have no idea on how to apply 
them to solve this. Perhaps I should declare indexOf as a 
template?

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Wed, Jun 12, 2019 at 07:46:12PM +0000, Mek101 via Digitalmars-d-learn wrote:
[...]
 public size_t indexOf(alias pred = "a == b", Range)(Range array)
 {
 	alias predicate = unaryFun!pred;
 	for(size_t i = 0; i < array.length; i++)
 		if(predicate(array[i]))
 			return i;
 	return size_t.max;
 }

 
 Say that I may want to use the function in a  nogc scope, providing a
  nogc callable, but I also want to reuse the same code in managed
 scope while passing a delegate: how can I apply the attributes of the
 given callable to the function so that they're automatically
 determined at compile time?

[...]

You don't need to do anything special; indexOf, as you declared it, is
already a template function, so the compiler should automatically apply
attribute inference to it. So if pred is  nogc, and the implementation
of indexOf itself doesn't invoke the GC, the compiler should
automatically infer  nogc for you.

One safeguard that you might want to consider is to write a  nogc
unittest, something like this:

	 nogc unittest
	{
		...
		auto result = indexOf!(...)(...);
		...
	}

The  nogc annotation on the unittest ensures that as long as the pred
argument to indexOf is  nogc, indexOf itself will also be  nogc. This
prevents future changes from accidentally introducing GC dependent code
in the implementation of indexOf, while at the same time not explicitly
marking indexOf as  nogc (only the unittest is annotated, not the
function itself) allows you to use it with GC-dependent predicates as
well.


T

-- 
Which is worse: ignorance or apathy? Who knows? Who cares? -- Erich Schubert

Mek101 <oidgemek101 gmail.com> writes:

I didn't know it applied to templates other than lambdas.

Thank you for your explanation.

Jacob Carlborg <doob me.com> writes:

On 2019-06-12 22:42, Mek101 wrote:
 I didn't know it applied to templates other than lambdas.
 
 Thank you for your explanation.

It applies to templates, lambdas (which basically are templates) and 
nested functions.

-- 
/Jacob Carlborg

Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:

On Thursday, June 13, 2019 3:49:04 AM MDT Jacob Carlborg via Digitalmars-d-
learn wrote:
 On 2019-06-12 22:42, Mek101 wrote:
 I didn't know it applied to templates other than lambdas.

 Thank you for your explanation.

 It applies to templates, lambdas (which basically are templates) and
 nested functions.

It also now applies to auto return functions, though that's a more recent
change.

- Jonathan M Davis