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package convert
import (
"github.com/zclconf/go-cty/cty"
)
// The current unify implementation is somewhat inefficient, but we accept this
// under the assumption that it will generally be used with small numbers of
// types and with types of reasonable complexity. However, it does have a
// "happy path" where all of the given types are equal.
//
// This function is likely to have poor performance in cases where any given
// types are very complex (lots of deeply-nested structures) or if the list
// of types itself is very large. In particular, it will walk the nested type
// structure under the given types several times, especially when given a
// list of types for which unification is not possible, since each permutation
// will be tried to determine that result.
func unify(types []cty.Type, unsafe bool) (cty.Type, []Conversion) {
if len(types) == 0 {
// Degenerate case
return cty.NilType, nil
}
prefOrder := sortTypes(types)
// sortTypes gives us an order where earlier items are preferable as
// our result type. We'll now walk through these and choose the first
// one we encounter for which conversions exist for all source types.
conversions := make([]Conversion, len(types))
Preferences:
for _, wantTypeIdx := range prefOrder {
wantType := types[wantTypeIdx]
for i, tryType := range types {
if i == wantTypeIdx {
// Don't need to convert our wanted type to itself
conversions[i] = nil
continue
}
if tryType.Equals(wantType) {
conversions[i] = nil
continue
}
if unsafe {
conversions[i] = GetConversionUnsafe(tryType, wantType)
} else {
conversions[i] = GetConversion(tryType, wantType)
}
if conversions[i] == nil {
// wantType is not a suitable unification type, so we'll
// try the next one in our preference order.
continue Preferences
}
}
return wantType, conversions
}
// TODO: For structural types, try to invent a new type that they
// can all be unified to, by unifying their respective attributes.
// If we fall out here, no unification is possible
return cty.NilType, nil
}
|
