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15c0b25d AP |
1 | package convert |
2 | ||
3 | import ( | |
107c1cdb | 4 | "errors" |
15c0b25d AP |
5 | |
6 | "github.com/zclconf/go-cty/cty" | |
7 | ) | |
8 | ||
9 | // This file contains the public interface of this package, which is intended | |
10 | // to be a small, convenient interface designed for easy integration into | |
11 | // a hypothetical language type checker and interpreter. | |
12 | ||
13 | // Conversion is a named function type representing a conversion from a | |
14 | // value of one type to a value of another type. | |
15 | // | |
16 | // The source type for a conversion is always the source type given to | |
17 | // the function that returned the Conversion, but there is no way to recover | |
18 | // that from a Conversion value itself. If a Conversion is given a value | |
19 | // that is not of its expected type (with the exception of DynamicPseudoType, | |
20 | // which is always supported) then the function may panic or produce undefined | |
21 | // results. | |
22 | type Conversion func(in cty.Value) (out cty.Value, err error) | |
23 | ||
24 | // GetConversion returns a Conversion between the given in and out Types if | |
25 | // a safe one is available, or returns nil otherwise. | |
26 | func GetConversion(in cty.Type, out cty.Type) Conversion { | |
27 | return retConversion(getConversion(in, out, false)) | |
28 | } | |
29 | ||
30 | // GetConversionUnsafe returns a Conversion between the given in and out Types | |
31 | // if either a safe or unsafe one is available, or returns nil otherwise. | |
32 | func GetConversionUnsafe(in cty.Type, out cty.Type) Conversion { | |
33 | return retConversion(getConversion(in, out, true)) | |
34 | } | |
35 | ||
36 | // Convert returns the result of converting the given value to the given type | |
37 | // if an safe or unsafe conversion is available, or returns an error if such a | |
38 | // conversion is impossible. | |
39 | // | |
40 | // This is a convenience wrapper around calling GetConversionUnsafe and then | |
41 | // immediately passing the given value to the resulting function. | |
42 | func Convert(in cty.Value, want cty.Type) (cty.Value, error) { | |
43 | if in.Type().Equals(want) { | |
44 | return in, nil | |
45 | } | |
46 | ||
47 | conv := GetConversionUnsafe(in.Type(), want) | |
48 | if conv == nil { | |
107c1cdb | 49 | return cty.NilVal, errors.New(MismatchMessage(in.Type(), want)) |
15c0b25d AP |
50 | } |
51 | return conv(in) | |
52 | } | |
53 | ||
54 | // Unify attempts to find the most general type that can be converted from | |
55 | // all of the given types. If this is possible, that type is returned along | |
56 | // with a slice of necessary conversions for some of the given types. | |
57 | // | |
58 | // If no common supertype can be found, this function returns cty.NilType and | |
59 | // a nil slice. | |
60 | // | |
61 | // If a common supertype *can* be found, the returned slice will always be | |
62 | // non-nil and will contain a non-nil conversion for each given type that | |
63 | // needs to be converted, with indices corresponding to the input slice. | |
64 | // Any given type that does *not* need conversion (because it is already of | |
65 | // the appropriate type) will have a nil Conversion. | |
66 | // | |
67 | // cty.DynamicPseudoType is, as usual, a special case. If the given type list | |
68 | // contains a mixture of dynamic and non-dynamic types, the dynamic types are | |
69 | // disregarded for type selection and a conversion is returned for them that | |
70 | // will attempt a late conversion of the given value to the target type, | |
71 | // failing with a conversion error if the eventual concrete type is not | |
72 | // compatible. If *all* given types are DynamicPseudoType, or in the | |
73 | // degenerate case of an empty slice of types, the returned type is itself | |
74 | // cty.DynamicPseudoType and no conversions are attempted. | |
75 | func Unify(types []cty.Type) (cty.Type, []Conversion) { | |
76 | return unify(types, false) | |
77 | } | |
78 | ||
79 | // UnifyUnsafe is the same as Unify except that it may return unsafe | |
80 | // conversions in situations where a safe conversion isn't also available. | |
81 | func UnifyUnsafe(types []cty.Type) (cty.Type, []Conversion) { | |
82 | return unify(types, true) | |
83 | } |