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56 lines
2.9 KiB
Markdown
56 lines
2.9 KiB
Markdown
# Compile Time Execution Problems (Metaprogramming)
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2016-11-02
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## Memory and Types
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Compile time execution (CTE) is a stage of the compiler which runs any Odin code the
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user requests before the creation of the executable. The data modified and generated
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by this stage will be used as the initialization data for the _compiled_ code.
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The CTE stage is an interpreter running the generated _single static assignment_ (SSA)
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tree for the requested code. When using the memory generated by the interpreter for the
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compiled code, there are a few problems. The main problem being: pointers will point
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to invalid memory addresses. This is becaused the memory space of the interpreter is
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completely different to the memory space of the executable (compiled code).
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The table below presents which data types are safe for transferal and which are not.
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Key:
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* Y - Yes
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* N - No
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* D - Dependent on elements
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* ? - Highly depends on a lot of factors (most likely no)
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| Type | Safe? |
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|-----------|------------------------------------------------------------------------|
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| boolean | Y |
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| integer | Y |
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| float | Y |
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| pointer | N - Maybe safe if never changed |
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| string | Y - Even though (ptr+int) interally, still safe to convert to constant |
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| any | N - (ptr+ptr) |
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| array | D |
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| vector | Y - Elements can only be boolean, integer, or float (thus safe) |
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| slice | N - Internally (ptr+int+int) |
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| maybe | D |
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| struct | D |
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| enum | Y |
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| union | N - (blob+int) |
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| raw_union | N - ^^^ |
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| tuple | D |
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| proc | ? - Need to solve the next problem |
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## Calling procedures (external and internal)
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If all the procedures are only from within the code itself, i.e. not a loaded pointer,
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then it is "safe". However, calling external procedures and passing procedures from the
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interpreter to external programs _will_ cause problems as many of the procedures are not
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stored in _real_ memory. This causes numerous problems.
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**TODO:**
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* Look at how other languages solve this problem (e.g. LUA)
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* ???
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