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Separate visibility for state variables and functions

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Nikita Stupin 2021-09-21 12:04:43 +03:00 committed by Kamil Śliwak
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commit 0f7b69432e
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docs/contracts/visibility-and-getters.rst
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@ -1,20 +1,41 @@
.. index:: ! visibility, external, public, private, internal
.. |visibility-caveat| replace:: Making something ``private`` or ``internal`` only prevents other contracts from reading or modifying the information, but it will still be visible to the whole world outside of the blockchain.
.. _visibility-and-getters:
**********************
Visibility and Getters
**********************
Solidity knows two kinds of function calls: internal
ones that do not create an actual EVM call (also called
a "message call") and external
ones that do. Because of that, there are four types of visibility for
functions and state variables.
State Variable Visibility
=========================
Functions have to be specified as being ``external``,
``public``, ``internal`` or ``private``.
For state variables, ``external`` is not possible.
``public``
Public state variables differ from internal ones only in that the compiler automatically generates
:ref:`getter functions<getter-functions>` for them, which allows other contracts to read their values.
When used within the same contract, the external access (e.g. ``this.x``) invokes the getter
while internal access (e.g. ``x``) gets the variable value directly from storage.
Setter functions are not generated so other contracts cannot directly modify their values.
``internal``
Internal state variables can only be accessed from within the contract they are defined in
and in derived contracts.
They cannot be accessed externally.
This is the default visibility level for state variables.
``private``
Private state variables are like internal ones but they are not visible in derived contracts.
.. warning::
|visibility-caveat|
Function Visibility
===================
Solidity knows two kinds of function calls: external ones that do create an actual EVM message call and internal ones that do not.
Furthermore, internal functions can be made inaccessible to derived contracts.
This gives rise to four types of visibility for functions.
``external``
External functions are part of the contract interface,
@ -24,27 +45,19 @@ For state variables, ``external`` is not possible.
``public``
Public functions are part of the contract interface
and can be either called internally or via
messages. For public state variables, an automatic getter
function (see below) is generated.
and can be either called internally or via message calls.
``internal``
Those functions and state variables can only be
accessed internally (i.e. from within the current contract
or contracts deriving from it), without using ``this``.
This is the default visibility level for state variables.
Internal functions can only be accessed from within the current contract
or contracts deriving from it.
They cannot be accessed externally.
Since they are not exposed to the outside through the contract's ABI, they can take parameters of internal types like mappings or storage references.
``private``
Private functions and state variables are only
visible for the contract they are defined in and not in
derived contracts.
Private functions are like internal ones but they are not visible in derived contracts.
.. note::
Everything that is inside a contract is visible to
all observers external to the blockchain. Making something ``private``
only prevents other contracts from reading or modifying
the information, but it will still be visible to the
whole world outside of the blockchain.
.. warning::
|visibility-caveat|
The visibility specifier is given after the type for
state variables and between parameter list and