aboutsummaryrefslogtreecommitdiffstats
path: root/docs/control-structures.rst
diff options
context:
space:
mode:
authorLeonardo Alt <leo@ethereum.org>2018-06-15 18:30:28 +0800
committerLeonardo Alt <leo@ethereum.org>2018-06-20 18:53:38 +0800
commit8862b3092bcdbcb8314ec27e2b11bf25fcc6346a (patch)
tree4570b3adc9678c944546144f5989629003422194 /docs/control-structures.rst
parentba7fbf11e72a4f9da149ac3c9b4c908e4f215250 (diff)
downloaddexon-solidity-8862b3092bcdbcb8314ec27e2b11bf25fcc6346a.tar.gz
dexon-solidity-8862b3092bcdbcb8314ec27e2b11bf25fcc6346a.tar.zst
dexon-solidity-8862b3092bcdbcb8314ec27e2b11bf25fcc6346a.zip
C99 scoping rules by default
Diffstat (limited to 'docs/control-structures.rst')
-rw-r--r--docs/control-structures.rst99
1 files changed, 22 insertions, 77 deletions
diff --git a/docs/control-structures.rst b/docs/control-structures.rst
index 7849d15a..cc1f7ca5 100644
--- a/docs/control-structures.rst
+++ b/docs/control-structures.rst
@@ -325,74 +325,7 @@ is ``false``. The default value for the ``uint`` or ``int`` types is ``0``. For
element will be initialized to the default value corresponding to its type. Finally, for dynamically-sized arrays, ``bytes``
and ``string``, the default value is an empty array or string.
-A variable declared anywhere within a function will be in scope for the *entire function*, regardless of where it is declared
-(this will change soon, see below).
-This happens because Solidity inherits its scoping rules from JavaScript.
-This is in contrast to many languages where variables are only scoped where they are declared until the end of the semantic block.
-As a result, the following code is illegal and cause the compiler to throw an error, ``Identifier already declared``:
-
-::
-
- // This will not compile
-
- pragma solidity ^0.4.16;
-
- contract ScopingErrors {
- function scoping() public {
- uint i = 0;
-
- while (i++ < 1) {
- uint same1 = 0;
- }
-
- while (i++ < 2) {
- uint same1 = 0;// Illegal, second declaration of same1
- }
- }
-
- function minimalScoping() public {
- {
- uint same2 = 0;
- }
-
- {
- uint same2 = 0;// Illegal, second declaration of same2
- }
- }
-
- function forLoopScoping() public {
- for (uint same3 = 0; same3 < 1; same3++) {
- }
-
- for (uint same3 = 0; same3 < 1; same3++) {// Illegal, second declaration of same3
- }
- }
- }
-
-In addition to this, if a variable is declared, it will be initialized at the beginning of the function to its default value.
-As a result, the following code is legal, despite being poorly written:
-
-::
-
- pragma solidity ^0.4.0;
-
- contract C {
- function foo() public pure returns (uint) {
- // baz is implicitly initialized as 0
- uint bar = 5;
- if (true) {
- bar += baz;
- } else {
- uint baz = 10;// never executes
- }
- return bar;// returns 5
- }
- }
-
-Scoping starting from Version 0.5.0
------------------------------------
-
-Starting from version 0.5.0, Solidity will change to the more widespread scoping rules of C99
+Scoping in Solidity follows the widespread scoping rules of C99
(and many other languages): Variables are visible from the point right after their declaration
until the end of a ``{ }``-block. As an exception to this rule, variables declared in the
initialization part of a for-loop are only visible until the end of the for-loop.
@@ -401,17 +334,12 @@ Variables and other items declared outside of a code block, for example function
user-defined types, etc., do not change their scoping behaviour. This means you can
use state variables before they are declared and call functions recursively.
-These rules are already introduced now as an experimental feature.
-
As a consequence, the following examples will compile without warnings, since
-the two variables have the same name but disjoint scopes. In non-0.5.0-mode,
-they have the same scope (the function ``minimalScoping``) and thus it does
-not compile there.
+the two variables have the same name but disjoint scopes.
::
- pragma solidity ^0.4.0;
- pragma experimental "v0.5.0";
+ pragma solidity >0.4.24;
contract C {
function minimalScoping() pure public {
{
@@ -430,8 +358,7 @@ In any case, you will get a warning about the outer variable being shadowed.
::
- pragma solidity ^0.4.0;
- pragma experimental "v0.5.0";
+ pragma solidity >0.4.24;
contract C {
function f() pure public returns (uint) {
uint x = 1;
@@ -443,6 +370,24 @@ In any case, you will get a warning about the outer variable being shadowed.
}
}
+.. warning::
+ Before version 0.5.0 Solidity followed the same scoping rules as JavaScript, that is, a variable declared anywhere within a function would be in scope
+ for the entire function, regardless where it was declared. Note that this is a breaking change. The following example shows a code snippet that used
+ to compile but leads to an error starting from version 0.5.0.
+
+ ::
+
+ // This will not compile
+
+ pragma solidity >0.4.24;
+ contract C {
+ function f() pure public returns (uint) {
+ x = 2;
+ uint x;
+ return x;
+ }
+ }
+
.. index:: ! exception, ! throw, ! assert, ! require, ! revert
Error handling: Assert, Require, Revert and Exceptions