millfork/docs/lang/types.md

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Types

Millfork puts extra limitations on which types can be used in which contexts.

Numeric types

• byte – 1-byte value of undefined signedness, defaulting to unsigned

• word – 2-byte value of undefined signedness, defaulting to unsigned (alias: int16)

• int24 – 3-byte value of undefined signedness, defaulting to unsigned (alias: farword; this alias is deprecated and might be removed in the future)

• long – 4-byte value of undefined signedness, defaulting to unsigned (alias: int32)

• int40, int48,... int128 – even larger types

• sbyte – signed 1-byte value

• ubyte – unsigned 1-byte value

• pointer – the same as word, but variables of this type default to be zero-page-allocated and you can index pointer variables (not arbitrary pointer-typed expressions though, f()[0] won't compile) You can create pointer values by suffixing .addr to the name of a variable, function or array.
  Work in progress: There's no reason to make a function return pointer yet, since currently to dereference it, you need to put it in a variable first anyway.

You can access single bytes of variables by using the following notations:

• for 2-byte-sized variables: .lo for the least significant byte and .hi for the most significant byte

• for larger variables: .b0 for the least significant byte and then .b1, .b2 and so on

You can also access words that are parts of variables:

• for 3-byte-sized variables: .loword is the word formed from .b1 and .b0 and .hiword is the word formed from .b2 and .b1

• for 4-byte-sized variables: .loword is the word formed from .b1 and .b0 and .hiword is the word formed from .b3 and .b2

Numeric types can be converted automatically:

• from a smaller type to a bigger type (byte→word)

• from a type of undefined signedness to a type of defined signedness (byte→sbyte)

• from a type of defined signedness to a type of undefined signedness (sbyte→byte)

Boolean types

TODO

Special types

• void – a unit type containing no information, can be only used as a return type for a function.

Enumerations

Enumeration is a 1-byte type that represents a set of values:

enum <name> { <variants, separated by commas or newlines> }

The first variant has value 0. Every next variant has a value increased by 1 compared to a previous one.

Alternatively, a variant can be given a custom constant value, which will change the sequence.

If there is at least one variant and no variant is given a custom constant value, then the enumeration is considered plain. Plain enumeration types can be used as array keys. For plain enumerations, a constant <name>.count is defined, equal to the number of variants in the enumeration.

Assigment between numeric types and enumerations is not possible without an explicit type cast:

enum E {}
byte b
E e
e = b       // won't compile
b = e       // won't compile
b = byte(e) // ok
e = E(b)    // ok

Plain enumerations have their variants equal to byte(0) to byte(<name>.count - 1).

Tip: You can use an enumeration with no variants as a strongly checked alternative byte type, as there are no checks no values when converting bytes to enumeration values and vice versa.