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Add some static array traits #924

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Add some static array traits #924

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106 changes: 106 additions & 0 deletions std/traits.d
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Original file line number Diff line number Diff line change
Expand Up @@ -5027,6 +5027,112 @@ unittest
//static assert( isAssociativeArray!EAA);
}


// Returns the element type of an array.
private alias _ArrayElementType(T : T[]) = T;
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@JakobOvrum JakobOvrum Oct 12, 2013

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I think it's strange that this matches for static array types. It's certainly not regular; if it's not a bug, it's an undocumented special case. I'm not sure if relying on this behaviour is a good idea, but the only code that would break is Phobos code so it's not a big deal.



/**
Gets the rank (number of dimensions) of a static array type.

If $(D T) isn't a static array assumes it to be a $(I zero-dimensional)
static array with single element and returns zero.
*/
template staticArrayDims(T)
{
static if(isStaticArray!T)
enum staticArrayDims = 1 + staticArrayDims!(_ArrayElementType!T);
else
enum staticArrayDims = 0;
}

///
unittest
{
static assert(staticArrayDims!int == 0);
static assert(staticArrayDims!(int[]) == 0);
static assert(staticArrayDims!(int[0]) == 1);
static assert(staticArrayDims!(int[7][8]) == 2);
static assert(staticArrayDims!(int[0][]) == 0);
static assert(staticArrayDims!(int[][0]) == 1);
}

unittest
{
static assert(staticArrayDims!string == 0);
static assert(staticArrayDims!(int[0][0]) == 2);
}


/**
Gets the element type of the innermost array in a multidimensional static array type.
Considers $(D T) to be an $(D n)-dimensional static array type.
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@JakobOvrum JakobOvrum Oct 12, 2013

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Why is this not statically enforced in the signature of the template?


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@andralex andralex Nov 19, 2012

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I've seen such functions for multidimensional arrays in other libs. Never found a good use for them.

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@andralex andralex Dec 8, 2012

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Thought more about this and a type InnermostType that goes all the way through static and dynamic dimension may be marginally useful and generic enough for inclusion in stdlib.

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@denis-sh denis-sh Dec 8, 2012

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As above I see no practical need to mix static and dynamic arrays. Again, our opinions are opposite.

If $(D T) isn't a static array assumes it to be a $(I zero-dimensional)
static array with single element and returns $(D T).
*/
template MultidimStaticArrayElementType(T, size_t n = staticArrayDims!T)
{
static assert(staticArrayDims!T >= n, "Not enough static array dimensions");
static if(n)
alias MultidimStaticArrayElementType = MultidimStaticArrayElementType!(_ArrayElementType!T, n-1);
else
alias MultidimStaticArrayElementType = T;
}

///
unittest
{
static assert(is(MultidimStaticArrayElementType!int == int));
static assert(is(MultidimStaticArrayElementType!(int[]) == int[]));
static assert(is(MultidimStaticArrayElementType!(int[0]) == int));
static assert(!__traits(compiles, MultidimStaticArrayElementType!(int[7][8], 3)));
static assert(is(MultidimStaticArrayElementType!(int[7][8]) == int));
static assert(is(MultidimStaticArrayElementType!(int[7][8], 1) == int[7]));
static assert(is(MultidimStaticArrayElementType!(int[7][8], 0) == int[7][8]));
static assert(is(MultidimStaticArrayElementType!(int[0][]) == int[0][]));
static assert(is(MultidimStaticArrayElementType!(int[][0]) == int[]));
}

unittest
{
static assert(is(MultidimStaticArrayElementType!string == string));
}


/**
Calculates the total element count of a multidimensional static array.
Considers $(D T) to be an $(D n)-dimensional static array type.

If $(D T) isn't a static array assumes it to be a $(I zero-dimensional)
static array with single element and returns 1.
*/
template multidimStaticArrayElementCount(T, size_t n = staticArrayDims!T)
{
static assert(staticArrayDims!T >= n, "Not enough static array dimensions");
enum multidimStaticArrayElementCount = T.sizeof / MultidimStaticArrayElementType!(T, n).sizeof;
}

///
unittest
{
static assert(multidimStaticArrayElementCount!int == 1);
static assert(multidimStaticArrayElementCount!(int[]) == 1);
static assert(multidimStaticArrayElementCount!(int[0]) == 0);
static assert(!__traits(compiles, multidimStaticArrayElementCount!(int[7][8], 3)));
static assert(multidimStaticArrayElementCount!(int[7][8]) == 7 * 8);
static assert(multidimStaticArrayElementCount!(int[7][8], 1) == 8);
static assert(multidimStaticArrayElementCount!(int[7][8], 0) == 1);
static assert(multidimStaticArrayElementCount!(int[0][]) == 1);
static assert(multidimStaticArrayElementCount!(int[][0]) == 0);
}

unittest
{
static assert(multidimStaticArrayElementCount!string == 1);
}


template isBuiltinType(T)
{
enum isBuiltinType = is(BuiltinTypeOf!T) && !isAggregateType!T;
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