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Update docs/contracts/abstract-contracts.rst.

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Alexander Arlt 2019-09-23 21:10:29 -05:00
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docs/contracts/abstract-contracts.rst
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@ -6,7 +6,11 @@
Abstract Contracts
******************
Contracts are marked as abstract when at least one of their functions lacks an implementation as in the following example (note that the function declaration header is terminated by ``;``)::
Contracts need to be marked as abstract when at least one of their functions was not implemented.
You can also mark contracts as abstract even though all functions are implemented.
This can be done by using the ``abstract`` keyword as shown in the following example. Note, that this contract need to be
defined as abstract, because the function ``utterance()`` was defined, but no implementation was
provided (no implementation body ``{ }`` was given).::
pragma solidity >=0.4.0 <0.7.0;
@ -14,7 +18,8 @@ Contracts are marked as abstract when at least one of their functions lacks an i
function utterance() public returns (bytes32);
}
Such contracts cannot be compiled (even if they contain implemented functions alongside non-implemented functions), but they can be used as base contracts::
Such abstract contracts can not be instantiated directly. This is also true, if an abstract contract itself does implement
all defined functions. The usage of an abstract contract as a base class is shown in the following example::
pragma solidity >=0.4.0 <0.7.0;
@ -26,7 +31,7 @@ Such contracts cannot be compiled (even if they contain implemented functions al
function utterance() public override returns (bytes32) { return "miaow"; }
}
If a contract inherits from an abstract contract and does not implement all non-implemented functions by overriding, it will itself be abstract.
If a contract inherits from an abstract contract and does not implement all non-implemented functions by overriding, it needs to be marked as abstract as well.
Note that a function without implementation is different from a :ref:`Function Type <function_types>` even though their syntax looks very similar.