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Merge pull request #12373 from ethereum/explainOperators

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Explanation about operators.
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chriseth 2021-12-15 18:37:41 +01:00 committed by GitHub
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docs/types/operators.rst
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@ -1,7 +1,35 @@
.. index:: assignment, ! delete, lvalue
.. index:: ! operator
Operators Involving LValues
===========================
Operators
=========
Arithmetic and bit operators can be applied even if the two operands do not have the same type.
For example, you can compute ``y = x + z``, where ``x`` is a ``uint8`` and ``z`` has
the type ``int32``. In these cases, the following mechanism will be used to determine
the type in which the operation is computed (this is important in case of overflow)
and the type of the operator's result:
1. If the type of the right operand can be implicitly converted to the type of the left
operand, use the type of the left operand,
2. if the type of the left operand can be implicitly converted to the type of the right
operand, use the type of the right operand,
3. otherwise, the operation is not allowed.
In case one of the operands is a :ref:`literal number <rational_literals>` it is first converted to its
"mobile type", which is the smallest type that can hold the value
(unsigned types of the same bit-width are considered "smaller" than the signed types).
If both are literal numbers, the operation is computed with arbitrary precision.
The operator's result type is the same as the type the operation is performed in,
except for comparison operators where the result is always ``bool``.
The operators ``**`` (exponentiation), ``<<`` and ``>>`` use the type of the
left operand for the operation and the result.
.. index:: assignment, lvalue, ! compound operators
Compound and Increment/Decrement Operators
------------------------------------------
If ``a`` is an LValue (i.e. a variable or something that can be assigned to), the
following operators are available as shorthands:
@ -12,6 +40,8 @@ to ``a += 1`` / ``a -= 1`` but the expression itself still has the previous valu
of ``a``. In contrast, ``--a`` and ``++a`` have the same effect on ``a`` but
return the value after the change.
.. index:: !delete
.. _delete:
delete