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| author | chriseth <chris@ethereum.org> | 2018-09-24 19:54:19 +0800 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2018-09-24 19:54:19 +0800 |
| commit | 2032953577a4755b36337bd102f5959a0ea652d3 (patch) | |
| tree | 60ddb24d1a0e8c7ac4c6c73a20c3e5aadfee3f1f /docs/types.rst | |
| parent | 32112d64801ce559f113ef597cc29469c0dab770 (diff) | |
| parent | fb8617f05958abb7e125e62e615f181be5f646f3 (diff) | |
| download | dexon-solidity-2032953577a4755b36337bd102f5959a0ea652d3.tar.gz dexon-solidity-2032953577a4755b36337bd102f5959a0ea652d3.tar.zst dexon-solidity-2032953577a4755b36337bd102f5959a0ea652d3.zip | |
Merge pull request #5025 from ethereum/refTypes
[DOCS] Update reference types.
Diffstat (limited to 'docs/types.rst')
| -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 b5e1daa0..ca1bd586 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, |