Why is this an issue?
Nested code blocks create new scopes where variables declared within are inaccessible from the outside, and their lifespan ends with the block.
Although this may appear beneficial, their usage within a function often suggests that the function is overloaded. Thus, it may violate the Single
Responsibility Principle, and the function needs to be broken down into smaller functions.
The presence of nested blocks that don’t affect the control flow might suggest possible mistakes in the code.
However, nested code blocks are acceptable when they encapsulate all statements within a switch (a case xxx: or a
default:) to prevent variable declarations from interfering with other cases.
How to fix it
The nested code blocks should be extracted into separate methods.
Code examples
Noncompliant code example
void f(Cache &c, int data) {
int value;
{ // Noncompliant
std::scoped_lock l(c.getMutex());
if (c.hasKey(data)) {
value = c.get(data);
} else {
value = compute(data);
c.set(data, value);
}
} // Releases the mutex
switch(value) {
case 1:
{ // Noncompliant, some statements are outside of the block
int result = compute(value);
save(result);
}
log();
break;
case 2:
// ...
}
}
Compliant solution
int getValue(Cache &c, int data) {
std::scoped_lock l(c.getMutex());
if (c.hasKey(data)) {
return c.get(data);
} else {
value = compute(data);
c.set(data, value);
return value;
}
}
void f(Cache &c, int data) {
int value = getValue(c, data);
switch(value) {
case 1:
{ // Compliant, limits the scope of "result"
int result = compute(value);
save(result);
log();
}
break;
case 2:
// ...
}
}
Resources
Documentation
