Generic data types

What generic types are

Generic types are type families — they group concrete elementary types under one name. They appear in IEC standard- library function signatures and let a function accept several related types without listing each one explicitly.

ABS(IN: ANY_NUM): ANY_NUM     (* ABS works on any signed numeric *)
SHL(IN: ANY_BIT, N: UINT): ANY_BIT  (* SHL works on any bit-string *)

You cannot declare a variable of a generic type. iCount : ANY_NUM is a syntax error. The generic types only exist in function-signature slots; the actual variable type must be a concrete elementary type.

The generic type hierarchy

ANY
├── ANY_DERIVED           (* user-defined STRUCT/ARRAY/enum *)
└── ANY_ELEMENTARY
    ├── ANY_MAGNITUDE
    │   ├── ANY_NUM
    │   │   ├── ANY_REAL
    │   │   │   ├── REAL
    │   │   │   └── LREAL
    │   │   └── ANY_INT
    │   │       ├── ANY_SIGNED       (* SINT, INT, DINT, LINT *)
    │   │       └── ANY_UNSIGNED     (* USINT, UINT, UDINT, ULINT *)
    │   └── TIME
    ├── ANY_BIT
    │   ├── BOOL
    │   ├── BYTE
    │   ├── WORD
    │   ├── DWORD
    │   └── LWORD
    ├── ANY_STRING
    │   ├── STRING
    │   └── WSTRING
    └── ANY_DATE
        ├── DATE
        ├── TIME_OF_DAY
        └── DATE_AND_TIME

A function declared as (IN: ANY_NUM) accepts any of the concrete types under ANY_NUM (so all INT, DINT, REAL, USINT, etc., but not BOOL or STRING).

Practical use — reading library signatures

When you call library.read_block("ABS") over MCP, the returned signature is:

ABS(IN: ANY_NUM): ANY_NUM

This means:

• Pass any concrete ANY_NUM value as IN.
• The return type is the same concrete type as IN. So ABS(iVar) (where iVar : INT) returns an INT; ABS(rVar) (where rVar : REAL) returns a REAL.

matiec resolves the generic at call time to the concrete type of the argument and emits a type-specific C function call.

Type-promotion does NOT happen automatically

Even though both INT and DINT are under ANY_INT, a function declared (IN: ANY_INT): ANY_INT does NOT mix them in one call. If you write:

result := MAX(iA, dwB);          (* INT + DINT — fails *)

matiec rejects the call because the two inputs disagree on the concrete ANY_INT resolution. You have to convert one side:

result := MAX(INT_TO_DINT(iA), dwB);

IEC reference

IEC 61131-3 third edition (2013), clause 6.4.2 — “Generic data types”.

matiec conformance

matiec implements the generic-type hierarchy as described. The library function signatures returned by library.read_block use generic-type names directly. The no-implicit-promotion rule is the recurring porting pain point — see the type-conversion functions page for the explicit <SRC>_TO_<DST> fixes.