Thread overview
Dollar identifiers in code-generating constructs
Jul 03
monkyyy
Jul 04
monkyyy
July 03

A dollar identifier is an Identifier with a $ at the end. In a code-generating construct (mixed-in mixin template and static foreach/static foreach_reverse) the $ is replaced by a number.

For a loop, it is the index of iteration.

For a mixin template, it is the number of mixin templates mixed in up until this point.


Example: loop

enum xs = ["A", "BC", "DEF"];
static foreach (x; xs)
{
    size_t l = x.length; // Error on "BC" and "DEF", already defined.
}
enum xs = ["A", "BC", "DEF"];
static foreach (x; xs)
{
    size_t l$ = x.length; // Good: becomes `l0`, `l1`, `l2`
}

Example: mixin template

mixin template mixMeIn(T)
{
    alias R = int delegate(T);
}

struct S
{
    mixin mixMeIn!int; // Okay
    mixin mixMeIn!int; // Error, `R` already defined
}
mixin template mixMeIn(T)
{
    alias R$ = int delegate(T);
}

struct S
{
    mixin mixMeIn!int; // Okay, defines `R0`
    mixin mixMeIn!int; // Okay, defines `R1`
}
July 03

On Wednesday, 3 July 2024 at 10:25:14 UTC, Quirin Schroll wrote:

>

A dollar identifier is an Identifier with a $ at the end. In a code-generating construct (mixed-in mixin template and static foreach/static foreach_reverse) the $ is replaced by a number.

[...]

is there a static foreach usecase where you cant use a index?

template innate(T,alias discirmintor){
  T innate;
}
static foreach(i,A;...){
  alias L(int i_:i)=innate(F!A,i);
}
July 04

On Wednesday, 3 July 2024 at 13:34:11 UTC, monkyyy wrote:

>

On Wednesday, 3 July 2024 at 10:25:14 UTC, Quirin Schroll wrote:

>

A dollar identifier is an Identifier with a $ at the end. In a code-generating construct (mixed-in mixin template and static foreach/static foreach_reverse) the $ is replaced by a number.

[...]

is there a static foreach usecase where you cant use a index?

template innate(T,alias discirmintor){
  T innate;
}
static foreach(i,A;...){
  alias L(int i_:i)=innate(F!A,i);
}

One can always use the index: mixin("size_t l", cast(int)i, " = ..."). This is a lot of boilerplate for something conceptually simple.

July 04

On Thursday, 4 July 2024 at 11:13:47 UTC, Quirin Schroll wrote:

>

On Wednesday, 3 July 2024 at 13:34:11 UTC, monkyyy wrote:

>

On Wednesday, 3 July 2024 at 10:25:14 UTC, Quirin Schroll wrote:

>

A dollar identifier is an Identifier with a $ at the end. In a code-generating construct (mixed-in mixin template and static foreach/static foreach_reverse) the $ is replaced by a number.

[...]

is there a static foreach usecase where you cant use a index?

template innate(T,alias discirmintor){
  T innate;
}
static foreach(i,A;...){
  alias L(int i_:i)=innate(F!A,i);
}

One can always use the index: mixin("size_t l", cast(int)i, " = ..."). This is a lot of boilerplate for something conceptually simple.

I think you can always also use template specialization and it should be faster to access then mixins and theres a handful of other benefits should as being able to pass them around as an overloadset

July 04

Maybe this isn’t worth it, as mixin Identifiers would supersede this.