84 lines
3.5 KiB
Go
84 lines
3.5 KiB
Go
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package convert
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import (
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"fmt"
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"github.com/zclconf/go-cty/cty"
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)
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// This file contains the public interface of this package, which is intended
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// to be a small, convenient interface designed for easy integration into
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// a hypothetical language type checker and interpreter.
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// Conversion is a named function type representing a conversion from a
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// value of one type to a value of another type.
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//
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// The source type for a conversion is always the source type given to
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// the function that returned the Conversion, but there is no way to recover
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// that from a Conversion value itself. If a Conversion is given a value
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// that is not of its expected type (with the exception of DynamicPseudoType,
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// which is always supported) then the function may panic or produce undefined
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// results.
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type Conversion func(in cty.Value) (out cty.Value, err error)
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// GetConversion returns a Conversion between the given in and out Types if
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// a safe one is available, or returns nil otherwise.
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func GetConversion(in cty.Type, out cty.Type) Conversion {
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return retConversion(getConversion(in, out, false))
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}
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// GetConversionUnsafe returns a Conversion between the given in and out Types
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// if either a safe or unsafe one is available, or returns nil otherwise.
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func GetConversionUnsafe(in cty.Type, out cty.Type) Conversion {
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return retConversion(getConversion(in, out, true))
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}
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// Convert returns the result of converting the given value to the given type
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// if an safe or unsafe conversion is available, or returns an error if such a
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// conversion is impossible.
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//
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// This is a convenience wrapper around calling GetConversionUnsafe and then
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// immediately passing the given value to the resulting function.
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func Convert(in cty.Value, want cty.Type) (cty.Value, error) {
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if in.Type().Equals(want) {
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return in, nil
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}
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conv := GetConversionUnsafe(in.Type(), want)
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if conv == nil {
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return cty.NilVal, fmt.Errorf("incorrect type; %s required", want.FriendlyName())
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}
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return conv(in)
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}
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// Unify attempts to find the most general type that can be converted from
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// all of the given types. If this is possible, that type is returned along
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// with a slice of necessary conversions for some of the given types.
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//
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// If no common supertype can be found, this function returns cty.NilType and
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// a nil slice.
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//
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// If a common supertype *can* be found, the returned slice will always be
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// non-nil and will contain a non-nil conversion for each given type that
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// needs to be converted, with indices corresponding to the input slice.
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// Any given type that does *not* need conversion (because it is already of
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// the appropriate type) will have a nil Conversion.
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//
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// cty.DynamicPseudoType is, as usual, a special case. If the given type list
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// contains a mixture of dynamic and non-dynamic types, the dynamic types are
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// disregarded for type selection and a conversion is returned for them that
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// will attempt a late conversion of the given value to the target type,
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// failing with a conversion error if the eventual concrete type is not
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// compatible. If *all* given types are DynamicPseudoType, or in the
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// degenerate case of an empty slice of types, the returned type is itself
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// cty.DynamicPseudoType and no conversions are attempted.
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func Unify(types []cty.Type) (cty.Type, []Conversion) {
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return unify(types, false)
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}
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// UnifyUnsafe is the same as Unify except that it may return unsafe
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// conversions in situations where a safe conversion isn't also available.
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func UnifyUnsafe(types []cty.Type) (cty.Type, []Conversion) {
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return unify(types, true)
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}
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