package defaults¶
Package defaults lets a Go library type declare schema defaults for its inputs in a type-safe, string-free way. A type lists them from a Defaults method, referring to its own fields directly:
func (f File) Defaults() []defaults.Default {
return []defaults.Default{
defaults.Value(f.Mode, 0o644),
defaults.Optional(f.CreateDirectory),
}
}
Value declares that a field left out of a body takes the given value, which the runtime fills in before the type's code runs and the plan renders as the real input. Optional declares that a field may be left out with no declared value; the type's code handles the zero value the decoder produces. A field with neither marker, and not declared as a pointer, is required.
Because the fields are real struct fields, the Go compiler checks that they exist, that a rename updates them, and that a Value default matches its field's type. unobin reads these declarations from source at compile time (goschema); the methods are never called, so a returned value identifies the rule but not its field, which the compiler supplies from source.
Types¶
type Default¶
Default is one declared input default, built by Value or Optional. It is opaque: an author builds it and returns it; unobin reads the declaration from source rather than from this value.
func Optional¶
Optional declares that field may be left out of a body, with the decoder's zero value standing in; nothing is filled in for it.
func Value¶
Value declares that field takes def when a body leaves it out. The shared type parameter ties the default to the field's type.