On Sunday, 23 February 2014 at 14:36:36 UTC, Arlon Brandy wrote:
Today I hit two problems essentially which got me thinking
about how structs are used in D by most of the code I've seen
so far. Both problems are in:
http://d.puremagic.com/issues/show_bug.cgi?id=9513
So the RedBlackTree create excessive copies of large structs
via binaryFun, that and the obvious workaround also
necessitates use of a template. It seems that people use
structs to indicate one of two things, they want a type they
can pass around and return by copy such as vectors/matrices
etc. or just a way to allocate something on the stack, usually
because of the need for deterministic resource handling or for
performance reasons.
One of the great things about the D is that it allows you to
specify with the type how it should be used by choosing struct
vs class, so you can say at the same time whether the data
should be stored on the heap and whether it should be passed by
copy or by reference.
It seems to me that it might nice also to have a sub-division
within the "struct" to allow the user to indicate a struct that
should be passed by reference also like a class. It could be
the same in every way except it's always passed by reference
and people would have to write their own dup or something for
when they want to copy it.
This could also solve the problem of:
functionWithRefParams(LargeStruct.init, LargeStruct.init)
These new structs would always be passed by reference, and I
guess lvalues would be transformed to temporary stack objects
by the compiler so that they never have to be copied. To me the
"scope ref" proposal looks a bit like C++ rvalue references and
I thought this might be simpler and more useful but I don't
know it's probably not a good idea.
There is also a work around (I can't remember who posted it
originally) but to move a struct to heap its basically:
struct T {}
T t;
T* ptrT = [t].ptr;
