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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/metamethods.md | 33 |
1 files changed, 17 insertions, 16 deletions
diff --git a/docs/metamethods.md b/docs/metamethods.md index 00f5395b..2366b0c6 100644 --- a/docs/metamethods.md +++ b/docs/metamethods.md @@ -21,6 +21,11 @@ behavior that is required for all types: of `equals` may be faster to compute than `compare` for certain types, such as tables. +- `hash(x:&T, type:&TypeInfo)->Int32`: Values are hashed when used as keys in a + table or set. Hashing is consistent with equality, so two values that are + equal _must_ hash to the same hash value, ideally in a way that makes it + unlikely that two different values will have the same hash value. + Metamethods are automatically defined for all user-defined structs, DSLs, and enums. At this time, metamethods may not be overridden. @@ -29,19 +34,15 @@ enums. At this time, metamethods may not be overridden. Due to the presence of pointers, arrays, tables, and functions, there are potentially a very large number of metamethods that would be required if _every_ type had its own set of metamethods. To reduce the amount of generated -code, we use generic metamethods, which are general-purpose functions that take -an automatically compiled format string and variable number of arguments that -describe how to run a metamethod for that type. As a simple example, if `foo` -is an array of `Foo` structs, which has a defined `as_text()` method, then -rather than define a separate `Foo_Array_as_text()` function which would be 99% -identical to a `Baz_Array_as_text()` function, we instead insert a call to -`as_text(&foo, colorize, $ArrayInfo(&Foo))` to convert a `[Foo]` array to a -string, and you call `as_text(&baz, colorize, $ArrayInfo(&Baz))` to convert a -`[Baz]` array to a string. The generic metamethod handles all the reusable -logic like "an array's string form starts with a '[', then iterates over the -items, getting the item's string form (whatever that is) and putting commas -between them". - -Similarly, to compare two tables, we would use `compare(&x, &y, -$TableInfo(&KeyType, &ValueType))`. Or to hash an array of arrays of type -`Foo`, we would use `hash(&foo, $ArrayInfo($ArrayInfo(&Foo)))`. +code, Tomo uses generic metamethods, which are general-purpose functions that +take an object pointer and a type info struct pointer that has metadata about +the object's type. That metadata is added automatically at compile time and +used to perform the appropriate operations. As an example, every array follows +the same logic when performing comparisons, except that each item is compared +using the item's comparison function. Therefore, we can compile a single array +comparison function and reuse it for each type of array if we pass in some +metadata about how to compare the array's items. + +When possible, we avoid calling metamethods (for example, doing fixed-sized +integer comparisons does not require calling a function), but metamethods are +available as a fallback or for working with container types or pointers. |