Casts

CAST declarations with function, implicit, assignment, and explicit cast contexts.

Implicit cast

SCHEMA public {
    CAST (mytype AS TEXT)
        WITH FUNCTION mytype_to_text(mytype)
        AS IMPLICIT;
}

-- emits
CREATE CAST (mytype AS text)
    WITH FUNCTION mytype_to_text(mytype)
    AS IMPLICIT;

Assignment cast

SCHEMA public {
    CAST (TEXT AS mytype)
        WITH FUNCTION text_to_mytype(TEXT)
        AS ASSIGNMENT;
}

-- emits
CREATE CAST (text AS mytype)
    WITH FUNCTION text_to_mytype(text)
    AS ASSIGNMENT;

Explicit cast (default)

SCHEMA public {
    CAST (mytype AS INTEGER)
        WITH FUNCTION mytype_to_int(mytype);
}

-- emits
CREATE CAST (mytype AS integer)
    WITH FUNCTION mytype_to_int(mytype);

INOUT cast

SCHEMA public {
    CAST (mytype AS TEXT) WITH INOUT;
}

-- emits
CREATE CAST (mytype AS text) WITH INOUT;

Diffing behaviour

Cast identity is (source_type, target_type). There is no ALTER CAST in PostgreSQL. Any property change emits DROP CAST + CREATE CAST — DESTRUCTIVE. Dependents are checked before the drop.