Re: Need for std.meta.isSame over __traits(isSame)
On Wednesday, 1 September 2021 at 23:04:18 UTC, Per Nordlöw wrote:
On Wednesday, 1 September 2021 at 22:51:40 UTC, Per Nordlöw
wrote:
Can somebody explain the need for
Ok, `__traits(isSame)` always returns false for values.
This is very unfortunate as `std.traits.isSame` is one of the
most used template instances in typical std.meta-programming
and has a noticeable impact on time and space complexity now
that AliasAssign-enabled versions of std.meta members have
removed the need for other costly recursive template patterns.
I suggest we add a new builtin trait that exactly mimics
std.traits.isSame or inline the calls to `isSame` in
`std.traits.meta`. This is gonna significantly speed up
functions in std.meta, for instance `staticIndexOf`,
`EraseAll`, `GenericReplace`, `ReplaceAll`, `Pack`.
I suggest to change the template signature instead:
```d
template isSame(Args...)
if (Args.length == 2)
{
enum isSame = __traits(isSame, Args[0], Args[1]);
}
```
The problem is not `__traits(isSame)`, it's more the
TemplateAliasParameter, as observed previously.
Re: Need for std.meta.isSame over __traits(isSame)
On Wednesday, 1 September 2021 at 22:51:40 UTC, Per Nordlöw wrote:
Can somebody explain the need for
```d
private template isSame(alias a, alias b)
{
static if (!is(typeof( && )) // at least one is an
rvalue
&& __traits(compiles, { enum isSame = a == b; }))
// c-t comparable
{
enum isSame = a == b;
}
else
{
enum isSame = __traits(isSame, a, b);
}
}
```
when there is already
```d
__traits(isSame, a, b)
```
?
Are there any cases where
```d
__traits(isSame, a, b)
```
doesn't have the same value as
```d
a == b
```
provided the static if expression above is true.
the traits does not work on literals passed by
_AliasTemplateParameter_.
```d
enum isSame1(alias a, alias b) = a == b;
enum isSame2(alias a, alias b) = __traits(isSame, a, b);
pragma(msg, isSame1!(0, 0)); // true
pragma(msg, isSame2!(0, 0)); // false
```
This looks a bit like a bug, because `__traits(isSame, 0, 0)`
yields `true`
Re: Need for std.meta.isSame over __traits(isSame)
On Wednesday, 1 September 2021 at 22:51:40 UTC, Per Nordlöw wrote: Can somebody explain the need for Ok, `__traits(isSame)` always returns false for values. This is very unfortunate as `std.traits.isSame` is one of the most used template instances in typical std.meta-programming and has a noticeable impact on time and space complexity now that AliasAssign-enabled versions of std.meta members have removed the need for other costly recursive template patterns. I suggest we add a new builtin trait that exactly mimics std.traits.isSame or inline the calls to `isSame` in `std.traits.meta`. This is gonna significantly speed up functions in std.meta, for instance `staticIndexOf`, `EraseAll`, `GenericReplace`, `ReplaceAll`, `Pack`.
Need for std.meta.isSame over __traits(isSame)
Can somebody explain the need for
```d
private template isSame(alias a, alias b)
{
static if (!is(typeof( && )) // at least one is an rvalue
&& __traits(compiles, { enum isSame = a == b; })) //
c-t comparable
{
enum isSame = a == b;
}
else
{
enum isSame = __traits(isSame, a, b);
}
}
```
when there is already
```d
__traits(isSame, a, b)
```
?
Are there any cases where
```d
__traits(isSame, a, b)
```
doesn't have the same value as
```d
a == b
```
provided the static if expression above is true.
