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digitalmars.D.learn - Confused by refusal to expand template

reply "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
Code:
	struct S {
		int f(K)(K x) {
			return 1;
		}
		void func(K)(inout(K) x) {
			auto h = f(x);
		}
	}
	void main() {
		S s;
		s.func("abc");	// This is line 44
	}

This refuses to compile:

test2.d(44): Error: template test2.S.func(K) does not match any function
template declaration
test2.d(44): Error: template test2.S.func(K) cannot deduce template function
from argument types !()(string)

Removing 'inout' fixes the problem. But I don't understand why.


T

-- 
Perhaps the most widespread illusion is that if we were in power we would
behave very differently from those who now hold it---when, in truth, in order
to get power we would have to become very much like them. -- Unknown
Mar 23 2012
next sibling parent Timon Gehr <timon.gehr gmx.ch> writes:
On 03/23/2012 11:52 PM, H. S. Teoh wrote:

 Code:
 	struct S {
 		int f(K)(K x) {
 			return 1;
 		}
 		void func(K)(inout(K) x) {
 			auto h = f(x);
 		}
 	}
 	void main() {
 		S s;
 		s.func("abc");	// This is line 44
 	}

 This refuses to compile:

 test2.d(44): Error: template test2.S.func(K) does not match any function
template declaration
 test2.d(44): Error: template test2.S.func(K) cannot deduce template function
from argument types !()(string)

 Removing 'inout' fixes the problem. But I don't understand why.


 T


You already brought this up IIRC. The IFTI matching algorithm is too 
weak. I think it should work.
Mar 23 2012
prev sibling parent reply David <d dav1d.de> writes:
Am 23.03.2012 23:52, schrieb H. S. Teoh:

 Code:
 	struct S {
 		int f(K)(K x) {
 			return 1;
 		}
 		void func(K)(inout(K) x) {
 			auto h = f(x);
 		}
 	}
 	void main() {
 		S s;
 		s.func("abc");	// This is line 44
 	}

 This refuses to compile:

 test2.d(44): Error: template test2.S.func(K) does not match any function
template declaration
 test2.d(44): Error: template test2.S.func(K) cannot deduce template function
from argument types !()(string)

 Removing 'inout' fixes the problem. But I don't understand why.


 T


I've never really used inout, but don't you need it also for the 
return-type? Furthermore you don't the the inout here, since this 
template does match const/immutable/nothing anyways.
Mar 23 2012
parent reply Timon Gehr <timon.gehr gmx.ch> writes:
On 03/23/2012 11:58 PM, David wrote:

 Am 23.03.2012 23:52, schrieb H. S. Teoh:

 Code:
 struct S {
 int f(K)(K x) {
 return 1;
 }
 void func(K)(inout(K) x) {
 auto h = f(x);
 }
 }
 void main() {
 S s;
 s.func("abc"); // This is line 44
 }

 This refuses to compile:

 test2.d(44): Error: template test2.S.func(K) does not match any
 function template declaration
 test2.d(44): Error: template test2.S.func(K) cannot deduce template
 function from argument types !()(string)

 Removing 'inout' fixes the problem. But I don't understand why.


 T


 I've never really used inout, but don't you need it also for the
 return-type?


Not any more (DMD 2.059). See 
http://d.puremagic.com/issues/show_bug.cgi?id=7105


 Furthermore you don't the the inout here, since this
 template does match const/immutable/nothing anyways.


His intention probably is to prevent multiple instantiation of a 
template based on different constness.
Mar 23 2012
parent "Kenji Hara" <k.hara.pg gmail.com> writes:
On Friday, 23 March 2012 at 23:01:43 UTC, Timon Gehr wrote:

 On 03/23/2012 11:58 PM, David wrote:

 Am 23.03.2012 23:52, schrieb H. S. Teoh:

 Code:
 struct S {
 int f(K)(K x) {
 return 1;
 }
 void func(K)(inout(K) x) {
 auto h = f(x);
 }
 }
 void main() {
 S s;
 s.func("abc"); // This is line 44
 }

 This refuses to compile:

 test2.d(44): Error: template test2.S.func(K) does not match 
 any
 function template declaration
 test2.d(44): Error: template test2.S.func(K) cannot deduce 
 template
 function from argument types !()(string)

 Removing 'inout' fixes the problem. But I don't understand 
 why.


 T


 I've never really used inout, but don't you need it also for 
 the
 return-type?


 Not any more (DMD 2.059). See 
 http://d.puremagic.com/issues/show_bug.cgi?id=7105


 Furthermore you don't the the inout here, since this
 template does match const/immutable/nothing anyways.


 His intention probably is to prevent multiple instantiation of 
 a template based on different constness.


This is definitely a bug. I've filed it in bugzilla, and posted a 
pull to fix it.
http://d.puremagic.com/issues/show_bug.cgi?id=7769
Mar 24 2012