From 6319a3fd067ace2cce7a22902cdc960e3df834ea Mon Sep 17 00:00:00 2001
From: Chris Ward <chriswhward@gmail.com>
Date: Thu, 12 Jul 2018 14:49:49 +0200
Subject: Move control structure related FAQ points
Updates from reviews
clarify returning structs, and move returning arrays and strings from separate section
Further clarifications
Updates from review
Final updates
---
docs/control-structures.rst | 27 ++++++++++++++++++++-------
docs/frequently-asked-questions.rst | 25 -------------------------
2 files changed, 20 insertions(+), 32 deletions(-)
diff --git a/docs/control-structures.rst b/docs/control-structures.rst
index 9da29d14..5e3b722b 100644
--- a/docs/control-structures.rst
+++ b/docs/control-structures.rst
@@ -2,7 +2,7 @@
Expressions and Control Structures
##################################
-.. index:: ! parameter, parameter;input, parameter;output
+.. index:: ! parameter, parameter;input, parameter;output, parameter;multiple
Input Parameters and Output Parameters
======================================
@@ -32,6 +32,8 @@ something like::
Input parameters can be used just as any other local variable
can be used, they can also be assigned to.
+.. index:: return array, return string, array, string, array of strings, dynamic array, variably sized array, return struct, struct
+
Output Parameters
-----------------
@@ -54,12 +56,21 @@ write::
}
The names of output parameters can be omitted.
-The output values can also be specified using ``return`` statements,
+The return values can be specified using ``return`` statements,
which are also capable of :ref:`returning multiple values<multi-return>`.
Return parameters can be used as any other local variable and they
are zero-initialized; if they are not explicitly
set, they stay zero.
+
+.. note::
+ You cannot return some types from non-internal functions, notably
+ multi-dimensional dynamic arrays and structs. If you enable the
+ new experimental ``ABIEncoderV2`` feature by adding ``pragma experimental
+ ABIEncoderV2;`` to your source file then more types are available, but
+ ``mapping`` types are still limited to inside a single contract and you
+ cannot transfer them.
+
.. index:: if, else, while, do/while, for, break, continue, return, switch, goto
Control Structures
@@ -120,8 +131,8 @@ External Function Calls
The expressions ``this.g(8);`` and ``c.g(2);`` (where ``c`` is a contract
instance) are also valid function calls, but this time, the function
will be called "externally", via a message call and not directly via jumps.
-Please note that function calls on ``this`` cannot be used in the constructor, as the
-actual contract has not been created yet.
+Please note that function calls on ``this`` cannot be used in the constructor,
+as the actual contract has not been created yet.
Functions of other contracts have to be called externally. For an external call,
all function arguments have to be copied to memory.
@@ -130,8 +141,10 @@ all function arguments have to be copied to memory.
A function call from one contract to another does not create its own transaction,
it is a message call as part of the overall transaction.
-When calling functions of other contracts, the amount of Wei sent with the call and
-the gas can be specified with special options ``.value()`` and ``.gas()``, respectively::
+When calling functions of other contracts, you can specify the amount of Wei or gas sent with the call with the special options ``.value()`` and ``.gas()``, respectively. Any Wei you send to the contract is added to the total balance of the contract:
+
+
+::
pragma solidity >=0.4.0 <0.6.0;
@@ -400,7 +413,7 @@ In any case, you will get a warning about the outer variable being shadowed.
}
}
-.. index:: ! exception, ! throw, ! assert, ! require, ! revert
+.. index:: ! exception, ! throw, ! assert, ! require, ! revert, ! errors
.. _assert-and-require:
diff --git a/docs/frequently-asked-questions.rst b/docs/frequently-asked-questions.rst
index 3e9a6aca..8b655b0d 100644
--- a/docs/frequently-asked-questions.rst
+++ b/docs/frequently-asked-questions.rst
@@ -38,11 +38,6 @@ has it (which includes `Remix <https://remix.ethereum.org/>`_), then
``contractname.kill.sendTransaction({from:eth.coinbase})``, just the same as my
examples.
-Can you return an array or a ``string`` from a solidity function call?
-======================================================================
-
-Yes. See `array_receiver_and_returner.sol <https://github.com/fivedogit/solidity-baby-steps/blob/master/contracts/60_array_receiver_and_returner.sol>`_.
-
Is it possible to in-line initialize an array like so: ``string[] myarray = ["a", "b"];``
=========================================================================================
@@ -61,11 +56,6 @@ Example::
}
}
-Can a contract function return a ``struct``?
-============================================
-
-Yes, but only in ``internal`` function calls or if ``pragma experimental "ABIEncoderV2";`` is used.
-
If I return an ``enum``, I only get integer values in web3.js. How to get the named values?
===========================================================================================
@@ -103,15 +93,6 @@ How do structs work?
See `struct_and_for_loop_tester.sol <https://github.com/fivedogit/solidity-baby-steps/blob/master/contracts/65_struct_and_for_loop_tester.sol>`_.
-How do for loops work?
-======================
-
-Very similar to JavaScript. Such as the following example:
-
-``for (uint i = 0; i < a.length; i ++) { a[i] = i; }``
-
-See `struct_and_for_loop_tester.sol <https://github.com/fivedogit/solidity-baby-steps/blob/master/contracts/65_struct_and_for_loop_tester.sol>`_.
-
What are some examples of basic string manipulation (``substring``, ``indexOf``, ``charAt``, etc)?
==================================================================================================
@@ -292,12 +273,6 @@ In this example::
}
}
-Can a contract function accept a two-dimensional array?
-=======================================================
-
-If you want to pass two-dimensional arrays across non-internal functions,
-you most likely need to use ``pragma experimental "ABIEncoderV2";``.
-
What is the relationship between ``bytes32`` and ``string``? Why is it that ``bytes32 somevar = "stringliteral";`` works and what does the saved 32-byte hex value mean?
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