I got another idea for how using C++ objects without no-arg constructors
could work. It means enforcing C++ variable scoping through compile-time
errors, but keeping Python syntax.
a) This gives compiler error: "CppObject has no no-arg constructor, but
is used before assigned to"
cdef CppObject obj
obj.a = 3
b) This works:
cdef CppObject obj
if foo:
obj = bar
obj.func()
del obj # note: introducing del, but only in a special case
else:
obj = bar2
obj.asdf()
del obj
c) Compiler error: "C++ object must be deleted before exiting block"
cdef CppObject obj
if foo:
obj = bar
obj.func()
d) Compiler error: "C++ object must be deleted within the same block"
cdef CppObject obj
if foo:
obj = bar
if True:
del obj
e) All variables are deleted on exit
cdef CppObject obj = bar
obj.func()
# end of function so don't require del
The transform necesarry to enforce these rules should not be too
complicated. I don't think we need full analysis, just track assignments
and deletions and usages on a per-name basis.
Finally, the C++ output is made by adding a block, i.e.
cdef CppObject obj
print 1
obj = bar
obj.func()
del obj
print 2
Results in
print 1
{
CppObject obj = bar;
obj.func()
} # del
print 2
Related: One must be able to call two-argument constructors on the stack
as well. This could e.g happen like this:
cdef CppObject obj
print 1
obj = CppObject(1,2) # or, obj = (1, 2)
which would translate to
print 1
{
CppObject obj(1,2);
...
}
--
Dag Sverre
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