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| -rw-r--r-- | docs/types.rst | 22 |
1 files changed, 14 insertions, 8 deletions
diff --git a/docs/types.rst b/docs/types.rst index c5ce4c31..ff99acaf 100644 --- a/docs/types.rst +++ b/docs/types.rst @@ -648,21 +648,27 @@ Another example that uses external function types:: .. index:: ! type;reference, ! reference type, storage, memory, location, array, struct Reference Types -================== +=============== -Complex types, i.e. types which do not always fit into 256 bits have to be handled -more carefully than the value-types we have already seen. Since copying -them can be quite expensive, we have to think about whether we want them to be -stored in **memory** (which is not persisting) or **storage** (where the state -variables are held). +Values of reference type can be modified through multiple different names. +Contrast this with value types where you get an independent copy whenever +a variable of value type is used. Because of that, reference types have to be handled +more carefully than value types. Currently, reference types comprise structs, +arrays and mappings. If you use a reference type, you always have to explicitly +provide the data area where the type is stored: ``memory`` (whose lifetime is limited +to a function call), ``storage`` (the location where the state variables are stored) +or ``calldata`` (special data location that contains the function arguments, +only available for external function call parameters). + +An assignment or type conversion that changes the data location will always incur an automatic copy operation, +while assignments inside the same data location only copy in some cases for storage types. .. _data-location: Data location ------------- - -Every complex type, i.e. *arrays* and *structs*, has an additional +Every reference type, i.e. *arrays* and *structs*, has an additional annotation, the "data location", about where it is stored. There are three data locations: ``memory``, ``storage`` and ``calldata``. Calldata is only valid for parameters of external contract functions and is required for this type of parameter. Calldata is a non-modifiable, |