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What causes this example of safeD code to be compiled in dmd and ldc but not compiled in gcc?
code :
immutable(int)* f(int* p) @trusted
{
version (none) p[2] = 13;
// Invalid. p[2] is out of bounds. This line would exhibit undefined
// behavior.
version (none) p[1] = 13;
// Invalid. In this program, p[1] happens to be in-bounds, so the
// line would not exhibit undefined behavior, but a trusted function
// is not allowed to rely on this.
version (none) return cast(immutable) p;
// Invalid. @safe code still has mutable access and could trigger
// undefined behavior by overwriting the value later on.
int* p2 = new int;
*p2 = 42;
return cast(immutable) p2;
// Valid. After f returns, no mutable aliases of p2 can exist.
}
void main() @safe
{
int[2] a = [10, 20];
int* mp = &a[0];
immutable(int)* ip = f(mp);
assert(a[1] == 20); // Guaranteed. f cannot access a[1].
assert(ip !is mp); // Guaranteed. f cannot introduce unsafe aliasing.
}
result code in gdc compiler :
main.d:25:15: error: cannot take address of local a in @safe function main
25 | int* mp = &a[0];
| ^
