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| 1 | namespace Semantic is | |
| 2 | use Source.LOCATION | |
| 3 | ||
| 4 | use Types.Type | |
| 5 | ||
| 6 | // Constraint-driven owner specialisation. Companion to | |
| 7 | // OWNER_TYPE_ARG_SPECIALIZER (which binds owner-generic args | |
| 8 | // from sibling actuals); this one binds from a downstream type | |
| 9 | // constraint already pushed onto the constructor expression. | |
| 10 | // | |
| 11 | // Three cases produce a binding: | |
| 12 | // | |
| 13 | // 1. Direct: the constraint's head Classy is the candidate's | |
| 14 | // owner. `let b: Box[int] = Box()` — constraint is | |
| 15 | // `Box[int]`, owner is `Box`, type_map comes straight from | |
| 16 | // the constraint's `type_map`. | |
| 17 | // | |
| 18 | // 2. Variant of constraint: the candidate's owner is a variant | |
| 19 | // of the constraint's union. `let m = MAYBE.SOME(42)` with | |
| 20 | // constraint `MAYBE[int]` — SOME inherits its parent's | |
| 21 | // argument_names (declare_variant passes them through), so | |
| 22 | // the union-keyed type_map's keys line up with the variant's | |
| 23 | // slots. | |
| 24 | // | |
| 25 | // 3. Ancestor unification: the constraint's head is an ancestor | |
| 26 | // of the candidate's owner. `class C[T]: Parent[T]` then | |
| 27 | // `let p: Parent[int] = C()`. We walk owner_classy's | |
| 28 | // ancestors; for any that's a generic of the constraint's | |
| 29 | // head with matching arity, line up ancestor formal slots | |
| 30 | // with constraint actuals and build a type_map keyed by | |
| 31 | // owner_classy's argument_names. | |
| 32 | // | |
| 33 | // The helper is stateless. Callers pass (candidate, constraint, | |
| 34 | // location) and get back either a specialised function or the | |
| 35 | // original candidate. Returning the original on any failure path | |
| 36 | // — not null — means the caller can chain | |
| 37 | // `_try_specialize_owner_with_placeholders` immediately after | |
| 38 | // without re-checking. | |
| 39 | class OWNER_CONSTRAINT_SPECIALIZER open is | |
| 40 | init() is | |
| 41 | super.init() | |
| 42 | si | |
| 43 | ||
| 44 | specialize_from_constraint( | |
| 45 | location: LOCATION, | |
| 46 | candidate: Symbols.Function, | |
| 47 | constraint: Type? | |
| 48 | ) -> Symbols.Function is | |
| 49 | if !constraint? then | |
| 50 | return candidate | |
| 51 | fi | |
| 52 | ||
| 53 | // The constraint was pushed down from an enclosing | |
| 54 | // expression on an earlier iteration and may embed | |
| 55 | // placeholders whose origins have since settled. | |
| 56 | // Specialising from the stale composite would commit a | |
| 57 | // placeholder-bearing owner - and an owner that is | |
| 58 | // already a Symbols.GENERIC short-circuits the phantom | |
| 59 | // registry, so nothing downstream would refresh it. | |
| 60 | let constraint_resolved = SETTLED_PLACEHOLDER_RESOLVER.instance.resolve(constraint) | |
| 61 | ||
| 62 | if isa Symbols.GENERIC(candidate.owner) then | |
| 63 | return candidate | |
| 64 | fi | |
| 65 | ||
| 66 | let owner_classy = cast Symbols.Classy?(candidate.owner) | |
| 67 | ||
| 68 | if !owner_classy? \/ !owner_classy.is_generic then | |
| 69 | return candidate | |
| 70 | fi | |
| 71 | ||
| 72 | let constraint_named = cast Types.NAMED?(constraint_resolved) | |
| 73 | ||
| 74 | if !constraint_named? then | |
| 75 | return candidate | |
| 76 | fi | |
| 77 | ||
| 78 | let constraint_generic = cast Symbols.GENERIC?(constraint_named.symbol) | |
| 79 | ||
| 80 | if !constraint_generic? then | |
| 81 | return candidate | |
| 82 | fi | |
| 83 | ||
| 84 | let is_direct = constraint_generic.symbol =~ owner_classy | |
| 85 | let is_variant_of_constraint = | |
| 86 | owner_classy.is_variant /\ | |
| 87 | cast Symbols.Symbol?(owner_classy.owner)! =~ constraint_generic.symbol | |
| 88 | ||
| 89 | let type_map: Collections.Map[Symbols.Symbol,Type] mut | |
| 90 | ||
| 91 | if is_direct then | |
| 92 | type_map = constraint_generic.type_map | |
| 93 | elif is_variant_of_constraint then | |
| 94 | // A variant declares type parameters of its own, distinct | |
| 95 | // from the union's even though it is declared with the | |
| 96 | // union's names. The constraint's map is keyed on the | |
| 97 | // union's parameters, so it is re-keyed onto the | |
| 98 | // variant's by position - the variant's slot i is the | |
| 99 | // union's slot i, which is what declare_variant passing | |
| 100 | // the union's names through means. | |
| 101 | let variant_map = Collections.MAP[Symbols.Symbol,Type]() | |
| 102 | ||
| 103 | for i in 0..owner_classy.argument_names.count do | |
| 104 | if i >= constraint_generic.arguments.count then | |
| 105 | return candidate | |
| 106 | fi | |
| 107 | ||
| 108 | let parameter = owner_classy.type_parameter_at(i) | |
| 109 | ||
| 110 | if !parameter? then | |
| 111 | return candidate | |
| 112 | fi | |
| 113 | ||
| 114 | variant_map[parameter] = constraint_generic.arguments[i] | |
| 115 | od | |
| 116 | ||
| 117 | type_map = variant_map | |
| 118 | else | |
| 119 | let unified = try_unify_via_ancestor(owner_classy, constraint_generic) | |
| 120 | ||
| 121 | if !unified? then | |
| 122 | return candidate | |
| 123 | fi | |
| 124 | ||
| 125 | type_map = unified | |
| 126 | fi | |
| 127 | ||
| 128 | let specialized_owner = Symbols.GENERIC.try_create_from(location, owner_classy, type_map) | |
| 129 | ||
| 130 | if !specialized_owner? then | |
| 131 | return candidate | |
| 132 | fi | |
| 133 | ||
| 134 | let specialized = specialized_owner.find_specialized_function(candidate) | |
| 135 | ||
| 136 | if !specialized? then | |
| 137 | return candidate | |
| 138 | fi | |
| 139 | ||
| 140 | return specialized | |
| 141 | si | |
| 142 | ||
| 143 | // Walk owner_classy's ancestor types looking for a generic | |
| 144 | // whose head matches `constraint_generic.symbol` and whose | |
| 145 | // argument count matches. For the first match, build a map | |
| 146 | // from owner_classy.argument_names to the constraint's | |
| 147 | // actual arguments by lining up the ancestor's | |
| 148 | // GenericArgument formals with positions in the constraint. | |
| 149 | // | |
| 150 | // Returns null when no ancestor matches or the alignment | |
| 151 | // doesn't cover every owner name (e.g. the ancestor reads | |
| 152 | // `Parent[(T, int)]` instead of `Parent[T]`). | |
| 153 | // | |
| 154 | // Exposed for unit testing in isolation; specialize_from_ | |
| 155 | // constraint calls it from the non-direct/non-variant path. | |
| 156 | try_unify_via_ancestor( | |
| 157 | owner_classy: Symbols.Classy, | |
| 158 | constraint_generic: Symbols.GENERIC | |
| 159 | ) -> Collections.Map[Symbols.Symbol,Type]? is | |
| 160 | for i in 0..owner_classy.ancestors.count do | |
| 161 | let ancestor = owner_classy.ancestors[i] | |
| 162 | ||
| 163 | if !isa Types.GENERIC(ancestor) then | |
| 164 | continue | |
| 165 | fi | |
| 166 | ||
| 167 | let ancestor_generic = ancestor | |
| 168 | let ancestor_symbol = cast Symbols.GENERIC?(ancestor_generic.symbol) | |
| 169 | ||
| 170 | if | |
| 171 | !ancestor_symbol? \/ | |
| 172 | !(ancestor_symbol.symbol =~ constraint_generic.symbol) \/ | |
| 173 | ancestor_generic.arguments.count != constraint_generic.arguments.count | |
| 174 | then | |
| 175 | continue | |
| 176 | fi | |
| 177 | ||
| 178 | let candidate = Collections.MAP[Symbols.Symbol,Type]() | |
| 179 | let ok mut = true | |
| 180 | ||
| 181 | for j in 0..ancestor_generic.arguments.count do | |
| 182 | let slot = ancestor_generic.arguments[j] | |
| 183 | ||
| 184 | if !isa Types.GenericArgument(slot) then | |
| 185 | ok = false | |
| 186 | break | |
| 187 | fi | |
| 188 | ||
| 189 | let arg = slot | |
| 190 | ||
| 191 | candidate[arg.symbol] = constraint_generic.arguments[j] | |
| 192 | od | |
| 193 | ||
| 194 | if !ok then | |
| 195 | continue | |
| 196 | fi | |
| 197 | ||
| 198 | for i in 0..owner_classy.argument_names.count do | |
| 199 | let parameter = owner_classy.type_parameter_at(i) | |
| 200 | ||
| 201 | if !parameter? \/ !candidate.contains_key(parameter) then | |
| 202 | ok = false | |
| 203 | break | |
| 204 | fi | |
| 205 | od | |
| 206 | ||
| 207 | if ok then | |
| 208 | return candidate | |
| 209 | fi | |
| 210 | od | |
| 211 | ||
| 212 | return null | |
| 213 | si | |
| 214 | si | |
| 215 | si |