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90 lines
2.8 KiB
Go
90 lines
2.8 KiB
Go
package cty
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import (
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"fmt"
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"reflect"
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)
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type capsuleType struct {
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typeImplSigil
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Name string
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GoType reflect.Type
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}
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func (t *capsuleType) Equals(other Type) bool {
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if otherP, ok := other.typeImpl.(*capsuleType); ok {
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// capsule types compare by pointer identity
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return otherP == t
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}
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return false
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}
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func (t *capsuleType) FriendlyName() string {
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return t.Name
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}
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func (t *capsuleType) GoString() string {
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// To get a useful representation of our native type requires some
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// shenanigans.
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victimVal := reflect.Zero(t.GoType)
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return fmt.Sprintf("cty.Capsule(%q, reflect.TypeOf(%#v))", t.Name, victimVal.Interface())
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}
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// Capsule creates a new Capsule type.
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//
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// A Capsule type is a special type that can be used to transport arbitrary
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// Go native values of a given type through the cty type system. A language
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// that uses cty as its type system might, for example, provide functions
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// that return capsule-typed values and then other functions that operate
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// on those values.
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//
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// From cty's perspective, Capsule types have a few interesting characteristics,
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// described in the following paragraphs.
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//
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// Each capsule type has an associated Go native type that it is able to
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// transport. Capsule types compare by identity, so each call to the
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// Capsule function creates an entirely-distinct cty Type, even if two calls
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// use the same native type.
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//
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// Each capsule-typed value contains a pointer to a value of the given native
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// type. A capsule-typed value supports no operations except equality, and
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// equality is implemented by pointer identity of the encapsulated pointer.
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//
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// The given name is used as the new type's "friendly name". This can be any
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// string in principle, but will usually be a short, all-lowercase name aimed
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// at users of the embedding language (i.e. not mention Go-specific details)
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// and will ideally not create ambiguity with any predefined cty type.
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//
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// Capsule types are never introduced by any standard cty operation, so a
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// calling application opts in to including them within its own type system
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// by creating them and introducing them via its own functions. At that point,
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// the application is responsible for dealing with any capsule-typed values
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// that might be returned.
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func Capsule(name string, nativeType reflect.Type) Type {
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return Type{
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&capsuleType{
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Name: name,
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GoType: nativeType,
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},
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}
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}
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// IsCapsuleType returns true if this type is a capsule type, as created
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// by cty.Capsule .
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func (t Type) IsCapsuleType() bool {
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_, ok := t.typeImpl.(*capsuleType)
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return ok
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}
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// EncapsulatedType returns the encapsulated native type of a capsule type,
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// or panics if the receiver is not a Capsule type.
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//
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// Is IsCapsuleType to determine if this method is safe to call.
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func (t Type) EncapsulatedType() reflect.Type {
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impl, ok := t.typeImpl.(*capsuleType)
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if !ok {
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panic("not a capsule type")
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}
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return impl.GoType
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}
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