Re: Trying to get type and name at compile time
On Tuesday, 24 May 2016 at 18:44:45 UTC, ag0aep6g wrote: Seems to be a problem in ApplyLeft: import std.meta: AliasSeq, ApplyLeft; alias addType(T, string name) = AliasSeq!(T, name); alias addTypeInt = ApplyLeft!(addType, int); alias FullyInstantiated = addTypeInt!"foo"; Fails with: "std/meta.d(1114): Error: cannot interpret int at compile time". I've filed an issue: https://issues.dlang.org/show_bug.cgi?id=16070 Thanks! I've worked around it for now with some recursion :) Using `is(...)` with an AliasSeq of only types is ok. But you can't use it when there's a non-type in the sequence. That makes sense. Thanks for the help, Edwin
Re: Trying to get type and name at compile time
On 05/24/2016 06:22 PM, Edwin van Leeuwen wrote:
That's what I assumed at first.. So why does the following fail with:
cannot interpret double at compile time? I assumed staticMap would
automatically flatten the resulting AliasSeqs.
```
import std.meta : AliasSeq, ApplyLeft, staticMap;
struct Point { double x; double y; }
template addType(T,alias name)
{
alias addType = AliasSeq!( typeof(__traits(getMember, Point, name)),
name );
}
alias test3 = addType!( Point, "x" );
// I expected AliasSeq!(double,"x")???
pragma(msg,test3); // tuple((double), "x")
//static assert(is(test == AliasSeq!(double,"x")));
alias ts = AliasSeq!("x","y");
alias addTypeP = ApplyLeft!(addType,Point);
alias mapped = staticMap!(addTypeP,ts);
pragma(msg,mapped);
void main() {
}
```
Seems to be a problem in ApplyLeft:
import std.meta: AliasSeq, ApplyLeft;
alias addType(T, string name) = AliasSeq!(T, name);
alias addTypeInt = ApplyLeft!(addType, int);
alias FullyInstantiated = addTypeInt!"foo";
Fails with: "std/meta.d(1114): Error: cannot interpret int at compile time".
I've filed an issue:
https://issues.dlang.org/show_bug.cgi?id=16070
[...]
I thought so, but a lot of the documentation does seem to compare it
(see the example here):
https://dlang.org/library/std/meta/static_map.html
Using `is(...)` with an AliasSeq of only types is ok. But you can't use
it when there's a non-type in the sequence.
Re: Trying to get type and name at compile time
On Tuesday, 24 May 2016 at 15:09:43 UTC, Adam D. Ruppe wrote:
On Tuesday, 24 May 2016 at 15:01:33 UTC, Edwin van Leeuwen
wrote:
// I expected AliasSeq!(double,"x")???
pragma(msg,test); // tuple((double), "x")
What Phobos calls AliasSeq is called tuple inside the compiler.
They are the same thing, just different names.
That's what I assumed at first.. So why does the following fail
with: cannot interpret double at compile time? I assumed
staticMap would automatically flatten the resulting AliasSeqs.
```
import std.meta : AliasSeq, ApplyLeft, staticMap;
struct Point { double x; double y; }
template addType(T,alias name)
{
alias addType = AliasSeq!( typeof(__traits(getMember, Point,
name)),
name );
}
alias test3 = addType!( Point, "x" );
// I expected AliasSeq!(double,"x")???
pragma(msg,test3); // tuple((double), "x")
//static assert(is(test == AliasSeq!(double,"x")));
alias ts = AliasSeq!("x","y");
alias addTypeP = ApplyLeft!(addType,Point);
alias mapped = staticMap!(addTypeP,ts);
pragma(msg,mapped);
void main() {
}
```
Looking at it now, I guess it is because staticMap does not work
with alias values, only with actual type lists. Is that correct?
Any ideas on how to do this?
static assert(is(test == AliasSeq!(double,"x")));
AliasSeq is not comparable as a type. You can test the
individual pieces of it (`is(test[0] == double) && test[1] ==
"x"`) or wrap it in a struct or something.
I thought so, but a lot of the documentation does seem to compare
it (see the example here):
https://dlang.org/library/std/meta/static_map.html
Re: Trying to get type and name at compile time
On Tuesday, 24 May 2016 at 15:01:33 UTC, Edwin van Leeuwen wrote: // I expected AliasSeq!(double,"x")??? pragma(msg,test); // tuple((double), "x") What Phobos calls AliasSeq is called tuple inside the compiler. They are the same thing, just different names. static assert(is(test == AliasSeq!(double,"x"))); AliasSeq is not comparable as a type. You can test the individual pieces of it (`is(test[0] == double) && test[1] == "x"`) or wrap it in a struct or something.
Trying to get type and name at compile time
Hi all,
I am trying to get the type and name of a field at compile time,
but can't get the following to work. Anyone any idea of why test
is not of the type AliasSeq!(double, "x")?
```
import std.meta : AliasSeq;
struct Point { double x; double y; }
alias test = AliasSeq!(
typeof(__traits(getMember, Point, "x")),
"x"
);
// I expected AliasSeq!(double,"x")???
pragma(msg,test); // tuple((double), "x")
static assert(is(test == AliasSeq!(double,"x")));
void main() {}
```
Cheers, Edwin
