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Rewrite std.meta.staticMap using AliasAssign #7756

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Rewrite std.meta.staticMap using AliasAssign #7756

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67 changes: 53 additions & 14 deletions std/meta.d
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Original file line number Diff line number Diff line change
Expand Up @@ -787,29 +787,68 @@ template DerivedToFront(TList...)
static assert(is(TL == AliasSeq!(C, B, A)));
}

private enum staticMapExpandFactor = 150;
private string generateCases()
version = UseAliasAssign; // use new alias assign feature to speed up recursive templates

version (UseAliasAssign)
{
string[staticMapExpandFactor] chunks;
chunks[0] = q{};
static foreach (enum i; 0 .. staticMapExpandFactor - 1)
chunks[i + 1] = chunks[i] ~ `F!(Args[` ~ i.stringof ~ `]),`;
string ret = `AliasSeq!(`;
foreach (chunk; chunks)
ret ~= `q{alias staticMap = AliasSeq!(` ~ chunk ~ `);},`;
return ret ~ `)`;
}
private alias staticMapBasicCases = AliasSeq!(mixin(generateCases()));
else
{
private enum staticMapExpandFactor = 150;
private string generateCases()
{
string[staticMapExpandFactor] chunks;
chunks[0] = q{};
static foreach (enum i; 0 .. staticMapExpandFactor - 1)
chunks[i + 1] = chunks[i] ~ `F!(Args[` ~ i.stringof ~ `]),`;
string ret = `AliasSeq!(`;
foreach (chunk; chunks)
ret ~= `q{alias staticMap = AliasSeq!(` ~ chunk ~ `);},`;
return ret ~ `)`;
}
private alias staticMapBasicCases = AliasSeq!(mixin(generateCases()));
}

/**
Evaluates to $(D AliasSeq!(F!(T[0]), F!(T[1]), ..., F!(T[$ - 1]))).
*/
template staticMap(alias F, Args ...)
{
static if (Args.length < staticMapExpandFactor)
mixin(staticMapBasicCases[Args.length]);
version (UseAliasAssign)
{
alias A = AliasSeq!();

static foreach (size_t i; 0 .. Args.length / 8)
{
A = AliasSeq!(A, F!(Args[i * 8 ]), F!(Args[i * 8 + 1]), F!(Args[i * 8 + 2]), F!(Args[i * 8 + 3]),
F!(Args[i * 8 + 4]), F!(Args[i * 8 + 5]), F!(Args[i * 8 + 6]), F!(Args[i * 8 + 7]));
}

enum n = Args.length & 7;
static if (n == 1)
A = AliasSeq!(A, F!(Args[$ - 1]));
else static if (n == 2)
A = AliasSeq!(A, F!(Args[$ - 2]), F!(Args[$ - 1]));
else static if (n == 3)
A = AliasSeq!(A, F!(Args[$ - 3]), F!(Args[$ - 2]), F!(Args[$ - 1]));
else static if (n == 4)
A = AliasSeq!(A, F!(Args[$ - 4]), F!(Args[$ - 3]), F!(Args[$ - 2]), F!(Args[$ - 1]));
else static if (n == 5)
A = AliasSeq!(A, F!(Args[$ - 5]), F!(Args[$ - 4]), F!(Args[$ - 3]), F!(Args[$ - 2]), F!(Args[$ - 1]));
else static if (n == 6)
A = AliasSeq!(A, F!(Args[$ - 6]), F!(Args[$ - 5]), F!(Args[$ - 4]), F!(Args[$ - 3]), F!(Args[$ - 2]), F!(Args[$ - 1]));
else static if (n == 7)
A = AliasSeq!(A, F!(Args[$ - 7]), F!(Args[$ - 6]), F!(Args[$ - 5]), F!(Args[$ - 4]), F!(Args[$ - 3]), F!(Args[$ - 2]), F!(Args[$ - 1]));

alias staticMap = A;
}
else
alias staticMap = AliasSeq!(staticMap!(F, Args[0 .. $/2]), staticMap!(F, Args[$/2 .. $]));
{
static if (Args.length < staticMapExpandFactor)
mixin(staticMapBasicCases[Args.length]);
else
alias staticMap = AliasSeq!(staticMap!(F, Args[0 .. $/2]), staticMap!(F, Args[$/2 .. $]));
}
}

///
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