92 lines
3.7 KiB
C++
92 lines
3.7 KiB
C++
/** @file GCObjectConversion.hpp
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*
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* @author Roland Conybeare, Jan 2026
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**/
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#pragma once
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#include <xo/gc/GCObject.hpp>
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#include <xo/alloc2/Allocator.hpp>
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#include <xo/facet/FacetRegistry.hpp>
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#include <xo/facet/obj.hpp>
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namespace xo {
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namespace scm {
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/** @brief compile-time conversion obj<AGCObject> <-> T
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*
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* Specialize for each T that participates in conversion.
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* Methods here aren't implemented
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**/
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template <typename T>
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struct GCObjectConversion {
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using AGCObject = xo::mm::AGCObject;
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using AAllocator = xo::mm::AAllocator;
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/** find gc-aware representation for @p x.
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* If necessary allocate from @p mm, but may
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* refer to @p x in-place
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**/
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static obj<AGCObject> to_gco(obj<AAllocator> mm, const T & x);
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/** convert to native representation @tparam T from gc-aware
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* @p gco. If necessary allocate from @p mm, but
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* may instead refer to @p x in-place
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**/
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static T from_gco(obj<AAllocator> mm, obj<AGCObject> gco);
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};
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/** Motivating use-case for GCObjectConversion is to transform
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* primitive function arguments and results to/from gc-aware
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* representation.
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*
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* However: Schematika also supports runtime polymorphism
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* which leads to primitives that expect obj<AFacet> arguments.
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*
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* Also, Schematika expression parser needs representation for
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* expressions, before type unification.
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*
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* Consider a function like:
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* def fact = lambda (n : i64) { if (n <= 0) then 1 else (n * fact(n - 1)); }
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* During expression parsing the rhs argument to multiply has unknown type.
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* To construct an expression for input to unification will use polymorphic
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* binding for multiply primitive, relying on specialization here for
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* its implementation.
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**/
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template <typename AFacet, typename DRepr>
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struct GCObjectConversion<obj<AFacet,DRepr>> {
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using AGCObject = xo::mm::AGCObject;
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using AAllocator = xo::mm::AAllocator;
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using FacetRegistry = xo::facet::FacetRegistry;
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using DVariantPlaceholder = xo::facet::DVariantPlaceholder;
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static obj<AGCObject> to_gco(obj<AAllocator>,
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obj<AFacet,DRepr> gco) {
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if constexpr (std::is_same_v<AFacet, AGCObject>) {
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// trivial conversion!
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return gco;
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} else if constexpr (std::is_same_v<DRepr, DVariantPlaceholder>) {
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// runtime polymorphism
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return FacetRegistry::instance().variant<AGCObject,AFacet>(gco);
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} else /* DRepr != DVariantPlaceholder */ {
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// known content w/ fat object pointer
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return obj<AGCObject,DRepr>(gco.data());
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}
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}
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static obj<AFacet,DRepr> from_gco(obj<AAllocator>,
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obj<AGCObject> gco) {
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if constexpr (std::is_same_v<AFacet, AGCObject>) {
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// trivial conversion
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return gco;
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} else {
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// both runtime and comptime polymorphism
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// use same path here, since representation of @p gco
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// is type-erased here
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return FacetRegistry::instance().variant<AFacet,AGCObject>(gco);
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}
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}
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};
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} /*namespace scm */
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} /*namespace xo*/
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/* end GCObjectConversion.hpp */
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