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/**
This module contains compiler support for casting dynamic arrays
Copyright: Copyright Digital Mars 2000 - 2019.
License: Distributed under the
$(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost Software License 1.0).
(See accompanying file LICENSE)
Source: $(DRUNTIMESRC core/internal/_array/_casting.d)
*/
module core.internal.array.casting;
/**
Used by `__ArrayCast` to emit a descriptive error message.
It is a template so it can be used by `__ArrayCast` in -betterC
builds. It is separate from `__ArrayCast` to minimize code
bloat.
Params:
fromType = name of the type being cast from
fromSize = total size in bytes of the array being cast from
fromLength = length of array being cast from
toType = name of the type being cast to
toElemSize = element size of array being cast to
*/
private void onArrayCastError()(string fromType, size_t fromSize, size_t fromLength, string toType, size_t toElemSize) @trusted
{
import core.internal.string : unsignedToTempString;
import core.memory : pureMalloc;
// convert discontiguous `msgComponents` to contiguous string on the C heap
enum msgLength = 2048;
// note: never freed!
char* msg = cast(char *)pureMalloc(msgLength);
size_t index = 0;
void add(const(char)[] m)
{
import core.stdc.string : memcpy;
auto N = msgLength - 1 - index;
if (N > m.length)
N = m.length;
// prevent superfluous and betterC-unfriendly checks via direct memcpy
memcpy(msg + index, m.ptr, N);
index += N;
}
add("`");
add(fromType);
add("[]` of length ");
auto s = unsignedToTempString(fromLength);
add(s[]);
add(" cannot be cast to `");
add(toType);
add("[]` as its length in bytes (");
s = unsignedToTempString(fromSize);
add(s[]);
add(") is not a multiple of `");
add(toType);
add(".sizeof` (");
s = unsignedToTempString(toElemSize);
add(s[]);
add(").");
msg[index] = '\0'; // null-termination
// first argument must evaluate to `false` at compile-time to maintain memory safety in release builds
assert(false, msg[0 .. index]);
}
/**
The compiler lowers expressions of `cast(TTo[])TFrom[]` to
this implementation. Note that this does not detect alignment problems.
Params:
from = the array to reinterpret-cast
Returns:
`from` reinterpreted as `TTo[]`
*/
TTo[] __ArrayCast(TFrom, TTo)(return scope TFrom[] from) @nogc pure @trusted
{
const fromSize = from.length * TFrom.sizeof;
const toLength = fromSize / TTo.sizeof;
if ((fromSize % TTo.sizeof) != 0)
{
onArrayCastError(TFrom.stringof, fromSize, from.length, TTo.stringof, TTo.sizeof);
}
struct Array
{
size_t length;
void* ptr;
}
auto a = cast(Array*)&from;
a.length = toLength; // jam new length
return *cast(TTo[]*)a;
}
@safe @nogc pure nothrow unittest
{
byte[int.sizeof * 3] b = cast(byte) 0xab;
int[] i;
short[] s;
i = __ArrayCast!(byte, int)(b);
assert(i.length == 3);
foreach (v; i)
assert(v == cast(int) 0xabab_abab);
s = __ArrayCast!(byte, short)(b);
assert(s.length == 6);
foreach (v; s)
assert(v == cast(short) 0xabab);
s = __ArrayCast!(int, short)(i);
assert(s.length == 6);
foreach (v; s)
assert(v == cast(short) 0xabab);
}
@system nothrow unittest
{
string msg;
try
{
auto str = "hello";
auto wstr = cast(wstring) str;
}
catch (Throwable t)
msg = t.msg;
static immutable expected = "`immutable(char)[]` of length 5 cannot be cast to `immutable(wchar)[]` as " ~
"its length in bytes (5) is not a multiple of `immutable(wchar).sizeof` (2).";
if (msg != expected)
{
import core.stdc.stdio;
printf("Expected: |%.*s|\n", cast(int) expected.length, expected.ptr);
printf("Actual : |%.*s|\n", cast(int) msg.length, msg.ptr);
assert(false);
}
}
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