[fpc-devel] Feature request/discussion - SetLengthNoInit

[J. Gareth Moreton]

Hi everyone,

This is something that came up in a discussion with a client. One thing 
he noticed when using SetLength with dynamic arrays is that it can cause 
a CPU bottleneck because it initialises the entire block to zero, which 
is often undesirable if the array is going to be overwritten with its 
own values (in his own example, he's passing the array to a GPU shader 
as an output buffer).  I mentioned that the best ways around this is to 
either pre-initialise the array and just reuse it where and when you 
need it (object pooling) or to use GetMem and FreeMem, which increases 
the danger of memory leaks, dangling pointers and removes the benefits 
of a managed type.

With all this in mind, would there be support for an intrinsic such as 
"SetLengthNoInit" or "SetLengthNoClear" or some similar name that has 
all the benefits of SetLength (especially the reference counting) but 
doesn't initialise new elements to zero? If I'm learning one thing, Free 
Pascal is finding a niche in some scientific applications, and speed can 
be essential sometimes.

Gareth aka. Kit


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