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[WIP] add extern (C++) struct Darray(T) and Dstring to simplify interop with C++ #7893

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[WIP] add extern (C++) struct Darray(T) and Dstring to simplify interop with C++ #7893

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89c737f
add extern (C++) struct Darray(T) to simplify interop with C++
timotheecour Feb 14, 2018
db47c80
fixup
timotheecour Feb 14, 2018
2c8005d
add visit(TypeVector t)
timotheecour Mar 15, 2018
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14 changes: 14 additions & 0 deletions src/dmd/cppmangle.d
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Original file line number Diff line number Diff line change
Expand Up @@ -877,6 +877,20 @@ public:
}
}

override void visit(TypeDArray t)
{
//if (substitute(t))
//return;

// from: template_args
buf.writestring("8__dslice");
buf.writeByte('I');
Type t2 = t.next;
assert(t2);
headOfType(t2);
buf.writeByte('E');
}
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@jacob-carlborg jacob-carlborg Mar 16, 2018

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I’ve been thinking how to implement this. The idea I had was to add a new method to the Type base class called typeForMangling, which takes a mangling as its argument and returns the type that should be used for that mangling. This allows a type to pose as another type during mangling. The T[] type would need to construct a DSlice!T type during the semantic phase. In this case, typeForMangling would be called when mangling T[] and use the mangling of the new type.

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@JohanEngelen JohanEngelen Mar 16, 2018

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[ this PR is now doing two things at once, or is this a cherry pick that is about to be merged? ]


override void visit(TypeSArray t)
{
if (t.isImmutable() || t.isShared())
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31 changes: 31 additions & 0 deletions src/dmd/interop.d
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@@ -0,0 +1,31 @@
/+
Example usage:
extern (C++) Dstring funLib(Dstring input)
{
import std.string : toUpper;
import std.conv : to;
return input.toNative.toUpper.to!Dstring;
}
+/

extern (C++) struct Darray(T)
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@marler8997 marler8997 Mar 16, 2018

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If you're going to create a wrapper type like this you'll probably need to do it in the same way that I've done in core.sentinel. Namely, you'll need to support implicit conversion from:

Darray!(immutable(char)) > Darray!(const(char))
Darray!char > Darray!(const(char))

You may also need to support implicit conversion to/from native D arrays, but implicit conversion between multiple types requires multiple alias this.

Take a look at core.sentinel to see how this is done.

{
size_t length;
T* ptr;

extern (D) this(T[] a)
{
this.length = a.length;
this.ptr = a.ptr;
}

extern (D) T[] toNative()
{
// TODO: could even use a raw cast since ABI is same
return ptr[0 .. length];
}
}

alias Dstring = Darray!char;
alias Dcstring = Darray!(const(char));
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@wilzbach wilzbach Mar 15, 2018

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alias string = immutable(char)[];, (though imho it should have been const(char), but I guess it's way too late to change that.)

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@timotheecour timotheecour Mar 15, 2018

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(resolved privately on slack https://dlang.slack.com/archives/D8ZMKRGUV/p1521139433000456)
TLDR: immutable has no C++ equivalent

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@wilzbach wilzbach Mar 15, 2018

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The slack conversation is private, so the link isn't helpful to other people.

in short: pragma(mangle) doesn't work in alias. It has been proposed in #7458, but closed due to inactivity :/

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@timotheecour timotheecour Mar 15, 2018

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not only that but pragma(mangle) wouldn't help with arbitrary array types even if it were implemented. this PR aims at supporting arbitrary D arrays, not just const(char)[] for example