falconGitHub

prefer-conditional-expressions

Same as prefer-conditional-expressions in Dart Code Metrics

Path
lint/complexity/prefer-conditional-expressions
Default
Off, opt in
Origin
Dart Code Metrics
Rule
325 of 512

Flags an if/else whose branches each reduce to a single return or a single assignment to the same target.

When both branches differ only in the value they return or assign, a conditional expression — return c ? a : b; or x = c ? a : b; — says the same thing in one line. The rule reports only the outermost if of a chain (whose parent is not an if and whose else is not an else if) where both branches reduce to a single return, or to a single assignment to the same variable. Local functions, closures, and labeled statements are included.

Invalid

example.dartdart
// Bad: a single assignment or single return in each branch.
String getStatus(bool isActive) {
  if (isActive) {
    return 'active';
  } else {
    return 'inactive';
  }
}

int getValue(bool hasValue) {
  if (hasValue)
    return 42;
  else
    return 0;
}

class Validator {
  bool isValid(String input) {
    if (input.isNotEmpty) {
      return true;
    } else {
      return false;
    }
  }
}

void setLabel(bool on) {
  String label;
  if (on) {
    label = 'on';
  } else {
    label = 'off';
  }
  print(label);
}
Prefer a conditional expression over an if/else with a single statement in each branch.
2String getStatus(bool isActive) {
3 if (isActive) {
Prefer a conditional expression over an if/else with a single statement in each branch.
10int getValue(bool hasValue) {
11 if (hasValue)
Prefer a conditional expression over an if/else with a single statement in each branch.
18 bool isValid(String input) {
19 if (input.isNotEmpty) {
Prefer a conditional expression over an if/else with a single statement in each branch.
28 String label;
29 if (on) {

Valid

example.dartdart
// Good: cases dart_code_linter's prefer-conditional-expressions does not flag.

String getStatus(bool isActive) {
  return isActive ? 'active' : 'inactive';
}

// Branches are calls, not a single assignment or return.
void printMessage(bool success) {
  if (success) {
    print('Success!');
  } else {
    print('Failed!');
  }
}

// else-if chains are skipped.
String classify(int code) {
  if (code == 0) {
    return 'zero';
  } else if (code == 1) {
    return 'one';
  } else {
    return 'many';
  }
}

// Assignments target different variables.
void assignDifferent(bool flag) {
  String x = '';
  String y = '';
  if (flag) {
    x = 'a';
  } else {
    y = 'b';
  }
  print('$x$y');
}

// Assignment target is not a simple identifier.
void assignIndex(bool flag, Map<String, int> m) {
  if (flag) {
    m['a'] = 1;
  } else {
    m['b'] = 2;
  }
}

// Multiple statements per branch.
void processData(bool flag) {
  if (flag) {
    print('Processing...');
    final result = compute();
    save(result);
  } else {
    cleanup();
  }
}

Configure prefer-conditional-expressions

Set its severity in falcon.json. See the configuration guide.

falcon.jsonjson
{
  "linter": {
    "rules": {
      "complexity": {
        "prefer-conditional-expressions": "error"
      }
    }
  }
}

Or silence one occurrence with a suppression comment; the reason is required.

example.dartdart
// falcon-ignore lint/complexity/prefer-conditional-expressions: <reason>