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90 lines
3.3 KiB
Markdown
90 lines
3.3 KiB
Markdown
[< back to index](../index.md)
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# Types
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Millfork puts extra limitations on which types can be used in which contexts.
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## Numeric types
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* `byte` – 1-byte value of undefined signedness, defaulting to unsigned
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* `word` – 2-byte value of undefined signedness, defaulting to unsigned
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(alias: `int16`)
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* `int24` – 3-byte value of undefined signedness, defaulting to unsigned
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(alias: `farword`; this alias is deprecated and might be removed in the future)
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* `long` – 4-byte value of undefined signedness, defaulting to unsigned
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(alias: `int32`)
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* `int40`, `int48`,... `int128` – even larger types
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* `sbyte` – signed 1-byte value
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* `ubyte` – unsigned 1-byte value
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* `pointer` – the same as `word`, but variables of this type default to be zero-page-allocated
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and you can index `pointer` variables (not arbitrary `pointer`-typed expressions though, `f()[0]` won't compile)
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You can create pointer values by suffixing `.addr` to the name of a variable, function or array.
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**Work in progress**:
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There's no reason to make a function return `pointer` yet, since currently to dereference it,
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you need to put it in a variable first anyway.
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You can access single bytes of variables by using the following notations:
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* for 2-byte-sized variables: `.lo` for the least significant byte and `.hi` for the most significant byte
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* for larger variables: `.b0` for the least significant byte and then `.b1`, `.b2` and so on
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You can also access words that are parts of variables:
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* for 3-byte-sized variables: `.loword` is the word formed from `.b1` and `.b0` and `.hiword` is the word formed from `.b2` and `.b1`
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* for 4-byte-sized variables: `.loword` is the word formed from `.b1` and `.b0` and `.hiword` is the word formed from `.b3` and `.b2`
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Numeric types can be converted automatically:
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* from a smaller type to a bigger type (`byte`→`word`)
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* from a type of undefined signedness to a type of defined signedness (`byte`→`sbyte`)
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* from a type of defined signedness to a type of undefined signedness (`sbyte`→`byte`)
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## Boolean types
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TODO
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## Special types
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* `void` – a unit type containing no information, can be only used as a return type for a function.
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## Enumerations
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Enumeration is a 1-byte type that represents a set of values:
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enum <name> { <variants, separated by commas or newlines> }
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The first variant has value 0. Every next variant has a value increased by 1 compared to a previous one.
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Alternatively, a variant can be given a custom constant value, which will change the sequence.
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If there is at least one variant and no variant is given a custom constant value,
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then the enumeration is considered _plain_. Plain enumeration types can be used as array keys.
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For plain enumerations, a constant `<name>.count` is defined,
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equal to the number of variants in the enumeration.
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Assigment between numeric types and enumerations is not possible without an explicit type cast:
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enum E {}
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byte b
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E e
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e = b // won't compile
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b = e // won't compile
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b = byte(e) // ok
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e = E(b) // ok
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Plain enumerations have their variants equal to `byte(0)` to `byte(<name>.count - 1)`.
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Tip: You can use an enumeration with no variants as a strongly checked alternative byte type,
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as there are no checks no values when converting bytes to enumeration values and vice versa.
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