• tcak (19/19) May 17 2015 [code]
• anonymous (18/39) May 17 2015 Per the template constraint, test needs a type D that implicitly

"tcak" <tcak gmail.com> writes:

[code]
void test(D)( const D data ) if( is(D: shared(char[]) ) ) { }

void main() {
	char[] text = new char[4];
	text[0] = 'a'; text[1] = 'b'; text[2] = 'c'; text[3] = 'd';
	
	auto t = cast( shared(const(char[])) )text[1..2];

	test( t );
}

[/code]

Error Message:
template main.test cannot deduce function from argument types 
!()(shared(const(char[])))

`t` is already shared(const(char[])), and `test` is expecting 
const shared(char[]). Aren't they already same?

--

Together with this question, I want to ask whether there is a way 
to check only being `shared`, only being `const`, or only being 
`char[]` of a template variable (D of `test` in this case)?

"anonymous" <anonymous example.com> writes:

On Sunday, 17 May 2015 at 21:34:21 UTC, tcak wrote:
 [code]
 void test(D)( const D data ) if( is(D: shared(char[]) ) ) { }

 void main() {
 	char[] text = new char[4];
 	text[0] = 'a'; text[1] = 'b'; text[2] = 'c'; text[3] = 'd';
 	
 	auto t = cast( shared(const(char[])) )text[1..2];

 	test( t );
 }

 [/code]

 Error Message:
 template main.test cannot deduce function from argument types 
 !()(shared(const(char[])))

 `t` is already shared(const(char[])), and `test` is expecting 
 const shared(char[]). Aren't they already same?

Per the template constraint, test needs a type D that implicitly 
converts to shared(char[]). Even when the top const is removed 
from typeof(t), there's still const in there: 
shared(const(char)[]). That isn't implicitly convertible to 
shared(char[]). Add const in the constraint and it works:
if( is(D: shared(const char[])) )

 --

 Together with this question, I want to ask whether there is a 
 way to check only being `shared`,

is(T == shared)

 only being `const`,

is(T == const)

 or only being `char[]`

I guess you mean to ignore any qualifiers of the array itself and 
the element type.

We have std.traits.Unqual, but that only removes qualifiers from 
the top level. As far as I know, we don't have anything like a 
DeepUnqual which would allow you to write is(DeepUnqual!T == 
char[]). You could write one.

Or you can get into the more advanced versions of the 
IsExpression:
is(T == E[], E) && is(Unqual!E == char)

 of a template variable (D of `test` in this case)?