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introduce tyInferred for the unbound concept type params

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* Why is tyInferred needed?

The bindings in TCandidate are capable of inferring types within a single
call expression. In concepts, we need to infer types in the same way, but
across the whole body of the concept.

Previously, once a concept type param was inferred, it was destructively
mutated using t.assignType, but this proved to be problematic in the presence
of overloads, because the bindings established while a non-matching overload
is tested must be reverted/forgotten. tyInferred offers a non-destructive way to
keep track of the inference progress.

While introducing new types usually requires a lot of code paths in the compiler
to updated, currently tyInferred is only a short-lived type within the concept body
pass and it's unlikely to introduce breakage elsewhere in the compiler.
This commit is contained in:
Zahary Karadjov 2016-08-02 01:15:46 +03:00
commit 8cd5f1f8f5
9 changed files with 126 additions and 96 deletions
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compiler/semasgn.nim
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@ -226,7 +226,7 @@ proc liftBodyAux(c: var TLiftCtx; t: PType; body, x, y: PNode) =
tyGenericParam, tyGenericBody, tyNil, tyExpr, tyStmt,
tyTypeDesc, tyGenericInvocation, tyForward:
internalError(c.info, "assignment requested for type: " & typeToString(t))
of tyOrdinal, tyRange,
of tyOrdinal, tyRange, tyInferred,
tyGenericInst, tyFieldAccessor, tyStatic, tyVar, tyAlias:
liftBodyAux(c, lastSon(t), body, x, y)
of tyUnused, tyUnused0, tyUnused1, tyUnused2: internalError("liftBodyAux")