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