22b4470f2a
Update all links to C++ Core Guidelines to `e49158a`.
Refresh done using the following script and some manual edits:
db76e34e74/personal/fred-tingaud/rspec/refresh-cppcoreguidelines.py
When re-using this script, be mindful that:
- it does not cover `shared_content`
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Co-authored-by: Marco Borgeaud <marco.borgeaud@sonarsource.com>
83 lines
3.3 KiB
Plaintext
83 lines
3.3 KiB
Plaintext
== Why is this an issue?
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There are three ways to initialize a non-static data member in a class:
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* With an in-class initializer
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* In the initialization list of a constructor
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* In the constructor body
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You should use those methods in that order of preference. When applicable, in-class initializers are best, because they apply automatically to all constructors of the class (except for default copy/move constructors and constructors where an explicit initialization for this member is provided). But they can only be used for initialization with constant values.
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If your member value depends on a parameter, you can initialize it in the constructor's initialization list. If the initialization is complex, you can define a function to compute the value, and use this function in the initializer list.
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Initialization in the constructor body has several issues. First, it's not an initialization, but an assignment. Which means it will not work with all data types (const-qualified members, members of reference type, member of a type without default constructor...). And even if it works, the member will first be initialized, then assigned to, which means useless operations will take place. To prevent "use-before-set" errors, it's better to immediately initialize the member with its real value.
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It's hard to find a good example where setting the value of a member in the constructor would be appropriate. One case might be when you assign to several data members in one operation. As a consequence constructor bodies are empty in many situations.
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This rules raises an issue in two conditions:
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* When you assign a value to a member variable in the body of a constructor.
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* When you initialize a member variable in the initializer list of a constructor, but could have done so directly in the class:
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** The initial value does not depend on a constructor parameter
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** The variable has either no in-class initializer, or an in-class initializer with the same value as in the constructor
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=== Noncompliant code example
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[source,cpp]
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----
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class S {
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int i1;
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int i2;
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int i3;
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public:
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S( int halfValue, int i2 = 0) : i2(i2), i3(42) { // Noncompliant for i1 and i3, compliant for i2
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this->i1 = 2*halfValue;
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}
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};
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----
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=== Compliant solution
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[source,cpp]
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----
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class S {
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int i1;
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int i2;
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int i3 = 42; // In-class initializer
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public:
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S( int halfValue, int i2 = 0 ) : i1(2*halfValue), i2(i2) {} // Compliant
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};
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----
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== Resources
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* {cpp} Core Guidelines - https://github.com/isocpp/CppCoreGuidelines/blob/e49158a/CppCoreGuidelines.md#c48-prefer-in-class-initializers-to-member-initializers-in-constructors-for-constant-initializers[C.48: Prefer in-class initializers to member initializers in constructors for constant initializers]
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* {cpp} Core Guidelines - https://github.com/isocpp/CppCoreGuidelines/blob/e49158a/CppCoreGuidelines.md#c49-prefer-initialization-to-assignment-in-constructors[C.49: Prefer initialization to assignment in constructors]
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ifdef::env-github,rspecator-view[]
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'''
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== Comments And Links
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(visible only on this page)
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=== duplicates: S3230
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=== on 2 Sep 2019, 22:15:24 Loïc Joly wrote:
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\[~geoffray.adde]: Can you please review my changes?
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=== on 23 Sep 2019, 11:20:25 Geoffray Adde wrote:
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As discussed, all fine by me.
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=== on 4 Oct 2019, 13:09:09 Geoffray Adde wrote:
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moved to previously existing RSPEC-3230
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endif::env-github,rspecator-view[]
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