Re: __traits(compiles , mixin ... )
On Wednesday, 25 October 2017 at 20:04:47 UTC, Adam D. Ruppe
wrote:
On Wednesday, 25 October 2017 at 19:50:31 UTC, SrMordred wrote:
so why this line resolves to false?
Because it is illegal to put a statement or declaration inside
__traits(compiles). sorry, I should have said that before...
even though the mixin can be legal in another context, it won't
be in the __traits context due to this:
https://dlang.org/spec/traits.html#compiles
"Returns a bool true if all of the arguments compile (are
semantically correct). The arguments can be symbols, types, or
expressions that are syntactically correct. The arguments
cannot be statements or declarations. "
When there's a closing ;, it is a mixin statement.
void F(){}
pragma(msg, __traits( compiles, mixin("F();") ) );//false
Oh, now thats explains. I thought that a "mixin statement" was
equal to the argument type that it compiles to. Thanks!
Re: __traits(compiles , mixin ... )
On Wednesday, 25 October 2017 at 19:50:31 UTC, SrMordred wrote:
so why this line resolves to false?
Because it is illegal to put a statement or declaration inside
__traits(compiles). sorry, I should have said that before... even
though the mixin can be legal in another context, it won't be in
the __traits context due to this:
https://dlang.org/spec/traits.html#compiles
"Returns a bool true if all of the arguments compile (are
semantically correct). The arguments can be symbols, types, or
expressions that are syntactically correct. The arguments cannot
be statements or declarations. "
When there's a closing ;, it is a mixin statement.
void F(){}
pragma(msg, __traits( compiles, mixin("F();") ) );//false
Re: __traits(compiles , mixin ... )
The semicolon there indicates it is a complete statement that
does nothing, and that's no error.
so why this line resolves to false?
void F(){}
pragma(msg, __traits( compiles, mixin("F();") ) );//false
Re: __traits(compiles , mixin ... )
On Wednesday, 25 October 2017 at 19:25:01 UTC, Adam D. Ruppe
wrote:
On Wednesday, 25 October 2017 at 19:12:02 UTC, SrMordred wrote:
Maybe i´m tired already, but whats wrong here:
pragma(msg, __traits( compiles, mixin("int x") ) );
You are missing a ;
The mixin must compile as a full thing in context. Variable
declarations need the ; to be complete.
it returns false anyway.
void F(){
writeln("inside");
}
struct T{}
void main()
{
pragma(msg, __traits( compiles, mixin("int x;") )
);//false
pragma(msg, __traits( compiles, mixin("F();") ) );//false
pragma(msg, __traits( compiles, mixin("F()") ) );//true
mixin( "F();" ); //compiles
pragma(msg, __traits( compiles, mixin("T();") ) ); //false
pragma(msg, __traits( compiles, mixin("T()") ) ); // true
mixin( "T();" ); // Error: `structliteral` has no effect in
expression `T()`
}
Re: __traits(compiles , mixin ... )
On Wednesday, 25 October 2017 at 19:21:27 UTC, SrMordred wrote: mixin( "T();" ); Error: `structliteral` has no effect in expression `T()` The semicolon there indicates it is a complete statement that does nothing, and that's no error. If there's no ;, it is just an expression that must be somewhere else - and the compile error is deferred until higher in the call chain.
Re: __traits(compiles , mixin ... )
On Wednesday, 25 October 2017 at 19:12:02 UTC, SrMordred wrote:
Maybe i´m tired already, but whats wrong here:
pragma(msg, __traits( compiles, mixin("int x") ) );
//output: false
Or the original case I found:
struct T{}
pragma(msg, __traits( compiles, T() ) ); //true
pragma(msg, __traits( compiles, mixin("T()") ) ); //true
mixin( "T();" ); Error: `structliteral` has no effect in
expression `T()`
Re: __traits(compiles , mixin ... )
On Wednesday, 25 October 2017 at 19:12:02 UTC, SrMordred wrote:
Maybe i´m tired already, but whats wrong here:
pragma(msg, __traits( compiles, mixin("int x") ) );
You are missing a ;
The mixin must compile as a full thing in context. Variable
declarations need the ; to be complete.
__traits(compiles , mixin ... )
Maybe i´m tired already, but whats wrong here:
pragma(msg, __traits( compiles, mixin("int x") ) );
//output: false
Re: __traits(compiles) + mixin
On Tuesday, 5 March 2013 at 07:53:15 UTC, cal wrote:
I'm confused about this:
import std.conv;
void main()
{
enum s = `1`.to!int;;
enum c = __traits(compiles, mixin({auto a = new
~s~;})); // line 1
mixin(auto a = ~s~;);
// line 2
}
This does not compile, giving errors about instantiating
std.conv.to!(int).to!(string). If I switch the order of lines 1
and 2 it compiles. Is this a bug or something I don't
understand about __traits(compiles)?
You can't test declarations inside of __traits(compiles), only
expressions. It's in the docs:
http://dlang.org/traits.html#compiles
Re: __traits(compiles) + mixin
On Tuesday, 5 March 2013 at 08:04:12 UTC, Andrej Mitrovic wrote:
You can't test declarations inside of __traits(compiles), only
expressions. It's in the docs:
http://dlang.org/traits.html#compiles
So why does this work:
import std.conv;
void main()
{
enum s = `1`.to!int;;
enum c = __traits(compiles, mixin({auto x = ~s~;})); //
true
}
Re: __traits(compiles) + mixin
On Tuesday, 5 March 2013 at 08:09:37 UTC, cal wrote:
On Tuesday, 5 March 2013 at 08:04:12 UTC, Andrej Mitrovic wrote:
You can't test declarations inside of __traits(compiles), only
expressions. It's in the docs:
http://dlang.org/traits.html#compiles
So why does this work:
import std.conv;
void main()
{
enum s = `1`.to!int;;
enum c = __traits(compiles, mixin({auto x = ~s~;})); //
true
}
Hmm.. And this also works:
enum c = __traits(compiles, mixin({auto a = new 1;}));
Something to do with CTFE combined with mixins?
Re: __traits(compiles) + mixin
On Tuesday, 5 March 2013 at 08:04:12 UTC, Andrej Mitrovic wrote:
On Tuesday, 5 March 2013 at 07:53:15 UTC, cal wrote:
I'm confused about this:
import std.conv;
void main()
{
enum s = `1`.to!int;;
enum c = __traits(compiles, mixin({auto a = new
~s~;})); // line 1
mixin(auto a = ~s~;);
// line 2
}
This does not compile, giving errors about instantiating
std.conv.to!(int).to!(string). If I switch the order of lines
1 and 2 it compiles. Is this a bug or something I don't
understand about __traits(compiles)?
You can't test declarations inside of __traits(compiles), only
expressions. It's in the docs:
http://dlang.org/traits.html#compiles
The errormessage is rather cryptic though.. Makes it look like
there is something with conv rather than compiles.
Re: __traits(compiles) + mixin
On 3/5/13, cal callumena...@gmail.com wrote:
So why does this work:
import std.conv;
void main()
{
enum s = `1`.to!int;;
enum c = __traits(compiles, mixin({auto x = ~s~;})); //
true
}
That's a function literal, i.e. an expression.
Re: __traits(compiles) + mixin
On Tuesday, 5 March 2013 at 08:14:58 UTC, simendsjo wrote:
Hmm.. And this also works:
enum c = __traits(compiles, mixin({auto a = new 1;}));
Something to do with CTFE combined with mixins?
But it gets this right, in that c is false. I had thought that by
wrapping the declaration in braces, making it a function, that
got around the 'no declarations' limitation.
Re: __traits(compiles) + mixin
On 03/05/2013 08:53 AM, cal wrote:
I'm confused about this:
import std.conv;
void main()
{
enum s = `1`.to!int;;
enum c = __traits(compiles, mixin({auto a = new ~s~;})); // line 1
mixin(auto a = ~s~;); // line 2
}
This does not compile, giving errors about instantiating
std.conv.to!(int).to!(string). If I switch the order of lines 1 and 2 it
compiles. Is this a bug or something I don't understand about
__traits(compiles)?
Compiles as expected with DMD 2.060. It is probably a regression.
Re: __traits(compiles) + mixin
On Tuesday, 5 March 2013 at 12:58:57 UTC, Timon Gehr wrote: Compiles as expected with DMD 2.060. It is probably a regression. Ah you're right, also with 2.061. I'll file.
__traits(compiles) + mixin
I'm confused about this:
import std.conv;
void main()
{
enum s = `1`.to!int;;
enum c = __traits(compiles, mixin({auto a = new ~s~;}));
// line 1
mixin(auto a = ~s~;);
// line 2
}
This does not compile, giving errors about instantiating
std.conv.to!(int).to!(string). If I switch the order of lines 1
and 2 it compiles. Is this a bug or something I don't understand
about __traits(compiles)?
is(typeof(mixin(X))) and __traits(compiles, mixin(X))
Is there a way to use string mixins with is(typeof(X)) and/or __traits(compiles, X)? As far as I can tell, if I do either of the following is(typeof(mixin(X))) __traits(compiles, mixin(X)) it does not mixin the string and test that for compilation but rather tests whether the mixin expression itself compiles. Is there way to actually test a mixed in string for compilation rather than the mixin expression itself? - Jonathan M Davis
Re: is(typeof(mixin(X))) and __traits(compiles, mixin(X))
On 2010-07-05 10.03, Jonathan M Davis wrote: Is there a way to use string mixins with is(typeof(X)) and/or __traits(compiles, X)? As far as I can tell, if I do either of the following is(typeof(mixin(X))) __traits(compiles, mixin(X)) it does not mixin the string and test that for compilation but rather tests whether the mixin expression itself compiles. Is there way to actually test a mixed in string for compilation rather than the mixin expression itself? - Jonathan M Davis Try to wrap the whole expression in the string mixin. -- Jacob Carlborg
