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Tom Lord <lord@xxxxxxx> writes: > Some of the functions defined in the interface, for example: > > scheme_value SCHEME_REAL_PART(scheme_value) (may GC) > > return a scheme_value as a C return value. > > This seems inherently error-prone. > > For example: > > x = SCHEME_CONS (SCHEME_REAL_PART (a), SCHEME_REAL_PART (b)); > > although a very natural seeming C statement, is incorrect code. SCM > makes that mistake (though its not a mistake within the goals of the > SCM project itself), Guile inherited it (where it really is a > mistake), and it proved to be a serious obstacle to, for example, > implementing either precise or copying GC. > > For starters, I would like to see all return values passed via > output parameters so that one would have to write: > > SCHEME_REAL_PART (&tmp1, a); > SCHEME_REAL_PART (&tmp2, b); > SCHEME_CONS (&x, tmp1, tmp2); > > In fact I'd go beyond that in a few ways -- but let me just start with > this and see where we get. This is one area where having explicitly-freed reference objects, as in the JNI, actually works better than the GC_PROTECT approach. With references, the first expression is perfectly fine --- assuming SCHEME_REAL_PART always returns a local reference.