One area where template bloat can be reduced is using cannonical symbol for alias parater forwarding. Let me explain with a sample of code :

template A(alias foo) {}
template B(alias foo) {
    alias afoo = A!foo;
}

B!symbol;

In this case, A is instanciated with B!symbol.foo as alias parameter, not symbol. This cause a huge amunt of useless template instanciation when compiling SDC (and can somtime cause infinite template instanciation that crash the compiler).


2013/6/10 Don Clugston <dclugston@gmail.com>

On 10 June 2013 02:28, Walter Bright <walter@digitalmars.com> wrote:

On 6/9/2013 1:32 PM, Don Clugston wrote:

Yeah. 4 orders of magnitude. Our codebase at sociomantic is a bit larger than Phobos + druntime, but it compiles in just a few seconds.
The problem is, that because of templates, the memory consumption isn't linear with source size.

dmd -unittest -o- std/algorithm

instantiates 344150 templates. Yes 344K. More than a third of a million.

Wow! (How many of those are unique, rather than reusing an existing instantiation?)

I'm not sure. That's the number of calls to the constructor of TemplateInstance. I don't understand the code well enough to know
if it can eventually gets merged with an existing TemplateInstance.
If so, then perhaps there's something we could do to prevent them from getting created in the first place if they are duplicates.
Certainly there are a huge number of instantiations of things like:
hasLength, isNarrowString, isForwardRange
It seems hard to believe there would be enough types to instantiate isNarrowString thousands of different times.


More than the number of lines of source in the module.
And yet there are only 1305 asserts in that module -- the tests are not particularly comprehensive.


-cov shows 96% coverage for std.algorithm

Yeah, my point was that for N tests, we get O(N^^2) templates instantiated.


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