Re: [boost] If one specifies a cxxstd-dialect, one must also specify the cxxstd

-----Original Message----- From: Boost On Behalf Of Edward Diener via Boost Sent: 12 February 2020 16:00 To: boost@lists.boost.org Cc: Edward Diener Subject: Re: [boost] If one specifies a cxxstd-dialect, one must also specify the cxxstd

On 2/12/2020 5:15 AM, Paul A Bristow via Boost wrote:

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-----Original Message----- From: Boost On Behalf Of Edward Diener via Boost Sent: 11 February 2020 18:32 To: boost@lists.boost.org Cc: Edward Diener Subject: Re: [boost] If one specifies a cxxstd-dialect, one must also specify the cxxstd

On 2/11/2020 4:56 AM, Paul A Bristow via Boost wrote:

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https://boostorg.github.io/build/manual/develop/index.html#bbv2.over vi ew.builtin s.features

says

5.3. Builtin features

cxxstd Allowed values: 98, 03, 0x, 11, 1y, 14, 1z, 17, 2a, latest.

cxxstd-dialect Allowed values: iso, gnu, ms.

So these work as expected

toolset=gcc cxxstd=2a cxxstd-dialect=gnu is OK toolset=gcc-9.2.0 cxxstd=2a cxxstd-dialect=gnu is OK too

But if I do NOT specify the cxxstd version - just

toolset=gcc cxxstd-dialect=gnu

for example:

boost\libs\multiprecision\example>b2 float128_snips toolset=gcc-8.1.0 cxxstd-dialect=gnu address-model=64 release > .mp_float128_snips_gcc810_14_gnu.log

Iboost/tools/build/src/build\feature.jam:1020: in feature.compress-subproperties from module feature error: assertion failure: [ set.equal "<cxxstd-dialect>gnu" "toolset-gcc:version8.1.0" : "toolset-gcc:version8.1.0" ] error: Expected: [ "true" ] error: Got: [ ]

which had be puzzled for a while.

Probably the even more common case of only having one compiler, say gcc, installed, and so not specifying toolset at all, confusingly behaves the same way?

This is a perfectly reasonable behaviour, but this requirement might helpfully be documented.

Or this more subtle than I understand?

"dialect" is a sub-feature of "cxxstd" in the same way that "version" is a sub-feature of "toolset". If you specify a sub-feature the feature to which it applies must always be specified somewhere.

I did say " perfectly reasonable behaviour" 😉

but if you say toolset=gcc you get a default version, and there isn't a command toolset-version=9.2, so the syntax isn't quite regular (and conveniently cleverer to you can write gcc-9.2.0 ...)

If you say cxxstd=xx you get a default dialect. Are you sure that you can not say toolset=gcc toolset-version=9.2 ? The "gcc-9.2.0" is shorthand for "toolset=gcc- 9.2.0" since Boost Build especially recognizes toolset designations without the need of "toolset=" syntax. You should be able to say "cxxstd=17-gnu" as an example, in order to specify both as feature-subfeature.

Correct!

b2 toolset=gcc cxxstd=17-gnu float128_snips

Neat - but I am not sure how I would have guessed, (without delving into .jam src).

b2 toolset=gcc toolset-version=9.2.0 cxxstd=17 float128_snips fails.

In the end it feels all too clever, mainly to reduce typing. I am not surprised to find that toolset=gcc-gnu doesn't work.

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Examples, examples ...

Are very helpful, as I have been bleating for over a decade. Thanks Paul