Hairy Pixels via fpc-devel wrote:
On Feb 1, 2023, at 5:56 PM, Adriaan van Os via fpc-devel
<fpc-devel@lists.freepascal.org> wrote:
"A const parameter is be passed by reference or (for small-sized parameters) by
value, whatever is most efficient. A constref parameter is guaranteed to be passed by
reference in all cases. The latter is therefore typically used for interfacing with
external code or when writing assembler routines."
I’ve been confused by constref versus const. I use constref when passing large
records as parameters so I know it will not make needless copies but why
doesn’t const function this way too? If the parameter is constant why would it
ever make sense for the compiler to copy the entire record when it knows the
function can’t change it?
Because, if e.g. the byte-size of a parameter is such that it fits into a CPU register, then
passing the parameter itself is more efficient than passing a reference to it. For large byte-size
parameters, const and constref function the same. The difference is with small byte-size parameters.
Regards,
Adriaan van Os
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