Types
Named types are declared with the syntax
type <id> = <type>
where <id> is an identifier and <type> is a type.
This creates a new type with the given name in the type system.
Type declarations must appear in the declaration section of a scope.
Any named type that appears in the body of a type declaration must be previously declared in the same scope or in an ancestor scope, i.e., types cannot contained forward references to other named types. In particular, named types cannot be recursive.
Note
A future version of SuperSQL may include recursive types. This is a research topic for the SuperDB project.
Input data may create named types that conflict with type declarations. In this case, a reference to a declared type in the query text uses the type definition of the nearest containing scope that binds the type name independent of types in the input.
When a named type is referenced as a string argument to cast, then any type definition with that name is ignored and the named type is bound to the type of the argument of cast. This does not affect the binding of the type used in other expressions in the query text.
Types can also be bound to identifiers without creating a named type using a constant declaration binding the name to a type value.
Examples
Cast integers to a network port type
# spq
type port=uint16
values this::port
# input
80
# expected output
80::(port=uint16)
Cast integers to a network port type calling cast with a type value
# spq
type port=uint16
values cast(this, <port>)
# input
80
# expected output
80::(port=uint16)
Override binding to type name with this
# spq
type foo=string
values cast(x, foo), cast(x, this.foo)
# input
{x:1,foo:<float64>}
{x:2,foo:<bool>}
# expected output
"1"::=foo
1.
"2"::=foo
true
A type name argument to cast in the form of a string is independent type declarations
# spq
type foo=string
values {str:cast(this, 'foo'), named:cast(this, foo)}
# input
1
2
# expected output
{str:1::=foo,named:"1"::=foo}
{str:2::=foo,named:"2"::=foo}
Bind a name to a type without creating a named type
# spq
const foo=<string>
values this::foo
# input
1
2
# expected output
"1"
"2"