[Scons-users] Compact notation

Andrew C. Morrow andrew.c.morrow at gmail.com
Mon Dec 12 10:50:26 EST 2016


Right, that is definitely an option. However, I was hoping to capitalize on
the logic for Append, Prepend, and more importantly AppendUnique and
PrependUnique.

How does the expansion of keyword arguments to a Builder work?

Can you pass a callable of some sort? If so, what is the signature? Does it
receive the containing environment?

Thanks,
Andrew


On Sun, Dec 11, 2016 at 5:18 PM, Eric Lunderberg <eric.lunderberg at gmail.com>
wrote:

> Well, it's not the prettiest, but you could manually generate the full
> list of CPPDEFINES in the python code.
>
> env.Library(
>     target="foo",
>     source=[
>         'source1.cpp',
>         'source2.cpp',
>         'source_windows.cpp' if windows else [],
>     ],
>     CPPDEFINES= env['CPPDEFINES'] +
>                 (["applies"] if windows else []),
>     LIBS=[
>         'lib1',
>         'lib2',
>         'lib_windows' if windows else [],
>     ]
> )
>
> The one problem with this is that it assumes that env['CPPDEFINES'] has
> been used before.  If you haven't, you'll get a KeyError, because
> env['CPPDEFINES'] hadn't been defined before.
>
> On Sun, Dec 11, 2016 at 5:01 PM, Andrew C. Morrow <
> andrew.c.morrow at gmail.com> wrote:
>
>>
>> Hi -
>>
>> Great suggestion! I just tried it, and it definitely works. Supporting
>> None would be nice too, as it seems a little clearer, but I can work
>> with [].
>>
>> OK, so that leaves question 2. Any ideas on a way to do accumulative
>> environment modifications inline when declaring a target?
>>
>> Thanks,
>> Andrew
>>
>> On Sun, Dec 11, 2016 at 11:27 AM, Brian Cody <brian.j.cody at gmail.com>
>> wrote:
>>
>>> Hey Andrew,
>>>
>>> For your first issue, does this work:
>>>
>>> env.Library(
>>>     target="foo",
>>>     source=[
>>>         'source1.cpp',
>>>         'source2.cpp',
>>>         'source_windows.cpp' if windows else [],
>>>     ],
>>>     LIBS=[
>>>         'lib1',
>>>         'lib2',
>>>         'lib_windows' if windows else [],
>>>     ]
>>> )
>>>
>>> I think it will automatically flatten the lists internally.
>>>
>>> On Sun, Dec 11, 2016 at 10:55 AM, Andrew C. Morrow <
>>> andrew.c.morrow at gmail.com> wrote:
>>>
>>>>
>>>> Over the past few years, I've encountered a few things that seem to
>>>> lead to more-verbose-than-needed python code when writing SConscripts,
>>>> leading to a less declarative feel. I've recently been thinking about how I
>>>> would want to write these things better. Perhaps others have encountered
>>>> these same issues and have found solutions?
>>>>
>>>> 1) Conditionally including a file or library:
>>>>
>>>> If I have a library that may or may not include a particular file (say,
>>>> based on if the target platform is windows), I generally need to pull the
>>>> list of sources out, and then conditionally append:
>>>>
>>>> fooSources=[
>>>>     'source1.cpp',
>>>>     'source2.cpp',
>>>> ]
>>>>
>>>> fooLibs=[
>>>>     'lib1',
>>>>     'lib2,
>>>> ]
>>>>
>>>> if windows:
>>>>    fooSources.append('source_windows.cpp')
>>>>    fooLibs.append('lib_windows')
>>>>
>>>> env.Library(
>>>>     target='foo',
>>>>     source=fooSources
>>>>     LIBS=fooLibs
>>>> )
>>>>
>>>> It would be nicer to write:
>>>>
>>>> env.Library(
>>>>     target="foo",
>>>>     source=[
>>>>         'source1.cpp',
>>>>         'source2.cpp',
>>>>         'source_windows.cpp' if windows else None,
>>>>     ],
>>>>     LIBS=[
>>>>         'lib1',
>>>>         'lib2',
>>>>         'lib_windows' if windows else None,
>>>>     ]
>>>> )
>>>>
>>>> But SCons seems to reject this:
>>>>
>>>> AttributeError: 'NoneType' object has no attribute 'name':
>>>>
>>>> Would it be a reasonable enhancement request that the various built-in
>>>> builders filter incoming lists for None? Is there another way to achieve
>>>> this? I could obviously attach filter each expression for None at the point
>>>> of its declaration, but that seems verbose.
>>>>
>>>> It doesn't come up often, but it would be nice.
>>>>
>>>>
>>>> 2) Inline manipulation of Environment variables.
>>>>
>>>> I can easily override an Env var when declaring a target:
>>>>
>>>> // Happens far away
>>>> env.Append(CPPDEFINES="whatever")
>>>>
>>>> env.Library(
>>>>     target="foo",
>>>>     source=...
>>>>     CPPDEFINES=["applies"]
>>>> )
>>>>
>>>> This will build with -Dapplies, overriding "whatever" in CPPDEFINES
>>>> for the sources in this target. But what if I want to Append or Prepend
>>>> (Unique), instead of override? There doesn't seem to be a compact syntax
>>>> for that. I need to write:
>>>>
>>>> // Happens far away
>>>> env.Append(CPPDEFINES=["whatever"])
>>>>
>>>> env = env.Clone()
>>>> env.AppendUnique(CPPDEFINES=["applies"])
>>>> env.Library(
>>>>     target="foo",
>>>>     source=...
>>>> )
>>>>
>>>> Now I get both -Dwhatever and -Dapplies for the sources.
>>>>
>>>> But what I'd really like to write is:
>>>>
>>>>
>>>> // Happens far away
>>>> env.Append(CPPDEFINES=["whatever"])
>>>>
>>>> env.Library(
>>>>     target="foo",
>>>>     source=...
>>>>     CPPDEFINES=UniqueAppender(["applies"]),
>>>> )
>>>>
>>>> Where UniqueAppender is a mutator that causes the effects of
>>>> env.AppendUnique(arg) to be applied to the local Environment for the target.
>>>>
>>>> Is there any existing mechanism to achieve this? If not, is it
>>>> possible? Reasonable? Other suggestions for how to do this?
>>>>
>>>> Combining the two techniques:
>>>>
>>>> Old:
>>>>
>>>> fooSources=[
>>>>     'source1.cpp',
>>>>     'source2.cpp',
>>>> ]
>>>>
>>>> fooLibs=[
>>>>     'lib1',
>>>>     'lib2,
>>>> ]
>>>>
>>>> if windows:
>>>>    fooSources.append('source_windows.cpp')
>>>>    fooLibs.append('lib_windows')
>>>>
>>>> env = env.Clone()
>>>> env.AppendUnique(CPPDEFINES=["applies"])
>>>> env.Library(
>>>>     target='foo',
>>>>     source=fooSources
>>>>     LIBS=fooLibs
>>>> )
>>>>
>>>> New (and making the 'applies' conditional as well, just for fun):
>>>>
>>>>
>>>> env.Library(
>>>>     target="foo",
>>>>     source=[
>>>>         'source1.cpp',
>>>>         'source2.cpp',
>>>>         'source_windows.cpp' if windows else None,
>>>>     ],
>>>>     CPPDEFINES=UniqueAppender([
>>>>         "applies" if windows else None,
>>>>     ]),
>>>>     LIBS=[
>>>>         'lib1',
>>>>         'lib2',
>>>>         'lib_windows' if windows else None,
>>>>     ]
>>>> )
>>>>
>>>> I think these two features would go a long way towards making complex
>>>> SConscripts more declarative.
>>>>
>>>> Thoughts? Suggestions? Ways I can do this now with SCons that I'm
>>>> missing?
>>>>
>>>> Thanks,
>>>> Andrew
>>>>
>>>>
>>>>
>>>> _______________________________________________
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>>>> Scons-users at scons.org
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>>>>
>>>>
>>>
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>>
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>
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