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## Groovy-ism Rules ("rulesets/groovyism.xml")

These are rules covering Groovy idiomatic usage, and Groovy-specific bad practices.

### AssignCollectionSort Rule

New in CodeNarc 0.15

The Collections.sort() method mutates the list and returns the list as a value. If you are assigning the result of sort() to a variable, then you probably don't realize that you're also modifying the original list as well. This is frequently the cause of subtle bugs. This violation is triggered when a sort() method call appears as the right hand side of an assignment, or when it appears as the first method call in a series of chained method calls.

Example of violations:

      def a = myList.sort()
      def b = myList.sort() { it }
      def c = myList.sort().findAll { x < 1 }

### AssignCollectionUnique Rule

New in CodeNarc 0.15

The Collections.unique() method mutates the list and returns the list as a value. If you are assigning the result of unique() to a variable, then you probably don't realize that you're also modifying the original list as well. This is frequently the cause of subtle bugs. This violation is triggered when a unique() method call appears as the right hand side of an assignment, or when it appears as the first method call in a series of chained method calls.

Example of violations:

      def a = myList.unique()
      def b = myList.unique() { it }
      def c = myList.unique().findAll { x < 1 }

### ClosureAsLastMethodParameter Rule

New in CodeNarc 0.14

If a method is called and the last parameter is an inline closure then it can be declared outside of the method call parentheses.

Example of violations:

        // creates violation: poor Groovy style
        [1,2,3].each({ println it })

        // no violation
        [1,2,3].each { println it }

### CollectAllIsDeprecated Rule

New in CodeNarc 0.16

The `collectAll` method is deprecated since Groovy 1.8.1. Use `collectNested` instead.

Example of violations:

    def list = [1, 2, [3, 4, [5, 6]], 7]

    list.collectAll { it * 2 }      // deprecated

    list.collectNested { it * 2 }   // replacement

### ConfusingMultipleReturns Rule

New in CodeNarc 0.16

Multiple return values can be used to set several variables at once. To use multiple return values, the left hand side of the assignment must be enclosed in parenthesis. If not, then you are not using multiple return values, you're only assigning the last element.

Example of violations:

    def a, b = [1, 2] // bad, b is null
    def c, d, e = [1, 2, 3] // bad, c and d are null
    class MyClass {
        def a, b, c = [1, 2, 3]  // bad, a and b are null
    }

    def x = 1              // ok
    def (f, g) = [1, 2]    // ok
    (a, b, c) = [1, 2, 3]  // ok

### ExplicitArrayListInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of `ArrayList`. In Groovy, it is best to write `new ArrayList() as []`, which creates the same object.

### ExplicitCallToAndMethod Rule

Since CodeNarc 0.11

This rule detects when the `and(Object)` method is called directly in code instead of using the `&` operator. A groovier way to express this: `a.and(b)` is this: `a & b`. This rule can be configured to ignore `this.and(Object)` using the ignoreThisReference property. It defaults to true, so even `and(x)` will not trigger a violation. The default is true because `and` appears commonly in Grails criteria.

This rule also ignores all calls to `super.and(Object)`.

### ExplicitCallToCompareToMethod Rule

Since CodeNarc 0.11

This rule detects when the `compareTo(Object)` method is called directly in code instead of using the <=>, >, >=, <, and <= operators. A groovier way to express this: `a.compareTo(b)` is this: `a <=> b`, or using the other operators. Here are some other ways to write groovier code:

        a.compareTo(b) == 0               // can be replaced by: a == b
        a.compareTo(b)                    // can be replaced by: a <=> b
        a.compareTo(b) > 0                // can be replaced by: a > b
        a.compareTo(b) >= 0               // can be replaced by: a >= b
        a.compareTo(b) < 0                // can be replaced by: a < b
        a.compareTo(b) <= 0               // can be replaced by: a <= b

This rule can be configured to ignore `this.compareTo(Object)` using the ignoreThisReference property. It defaults to `false`, so even `compareTo(x)` will trigger a violation.

This rule also ignores all calls to `super.compareTo(Object)`.

### ExplicitCallToDivMethod Rule

Since CodeNarc 0.11

This rule detects when the `div(Object)` method is called directly in code instead of using the `/` operator. A groovier way to express this: `a.div(b)` is this: `a / b`. This rule can be configured to ignore `div.xor(Object)` using the ignoreThisReference property. It defaults to false, so even `div(x)` will trigger a violation.

This rule also ignores all calls to `super.div(Object)`.

### ExplicitCallToEqualsMethod Rule

Since CodeNarc 0.11

This rule detects when the `equals(Object)` method is called directly in code instead of using the `==` or `!=` operator. A groovier way to express this: `a.equals(b)` is this: `a == b` and a groovier way to express : `!a.equals(b)` is: `a != b`. This rule can be configured to ignore `this.equals(Object)` using the ignoreThisReference property. It defaults to false, so even `equals(x)` will trigger a violation.

This rule also ignores all calls to `super.equals(Object)`.

### ExplicitCallToGetAtMethod Rule

Since CodeNarc 0.11

This rule detects when the `getAt(Object)` method is called directly in code instead of using the `[]` index operator. A groovier way to express this: `a.getAt(b)` is this: `a[b]`. This rule can be configured to ignore `this.getAt(Object)` using the ignoreThisReference property. It defaults to false, so even `getAt(x)` will trigger a violation.

This rule also ignores all calls to `super.getAt(Object)`.

### ExplicitCallToLeftShiftMethod Rule

Since CodeNarc 0.11

This rule detects when the `leftShift(Object)` method is called directly in code instead of using the << operator. A groovier way to express this: `a.leftShift(b)` is this: `a << b`. This rule can be configured to ignore `this.leftShift(Object)` using the ignoreThisReference property. It defaults to false, so even `leftShift(x)` will trigger a violation.

This rule also ignores all calls to `super.leftShift(Object)`.

### ExplicitCallToMinusMethod Rule

Since CodeNarc 0.11

This rule detects when the `minus(Object)` method is called directly in code instead of using the `-` operator. A groovier way to express this: `a.minus(b)` is this: `a - b`. This rule can be configured to ignore `minus.xor(Object)` using the ignoreThisReference property. It defaults to false, so even `minus(x)` will trigger a violation.

This rule also ignores all calls to `super.minus(Object)`.

### ExplicitCallToMultiplyMethod Rule

Since CodeNarc 0.11

This rule detects when the `multiply(Object)` method is called directly in code instead of using the `*` operator. A groovier way to express this: `a.multiply(b)` is this: `a * b`. This rule can be configured to ignore `this.multiply(Object)` using the ignoreThisReference property. It defaults to false, so even `multiply(x)` will trigger a violation.

This rule also ignores all calls to `super.multiply(Object)`.

### ExplicitCallToModMethod Rule

Since CodeNarc 0.11

This rule detects when the `mod(Object)` method is called directly in code instead of using the `%` operator. A groovier way to express this: `a.mod(b)` is this: `a % b`. This rule can be configured to ignore `this.mod(Object)` using the ignoreThisReference property. It defaults to false, so even `mod(x)` will trigger a violation.

This rule also ignores all calls to `super.mod(Object)`.

### ExplicitCallToOrMethod Rule

Since CodeNarc 0.11

This rule detects when the `or(Object)` method is called directly in code instead of using the `|` operator. A groovier way to express this: `a.or(b)` is this: `a | b`. This rule can be configured to ignore `this.or(Object)` using the ignoreThisReference property. It defaults to true, so even `or(x)` will not trigger a violation. This is the default because it is commonly used in Grails criteria.

This rule also ignores all calls to `super.or(Object)`.

### ExplicitCallToPlusMethod Rule

Since CodeNarc 0.11

This rule detects when the `plus(Object)` method is called directly in code instead of using the `+` operator. A groovier way to express this: `a.plus(b)` is this: `a + b`. This rule can be configured to ignore `this.plus(Object)` using the ignoreThisReference property. It defaults to false, so even `plus(x)` will trigger a violation.

This rule also ignores all calls to `super.plus(Object)`.

### ExplicitCallToPowerMethod Rule

Since CodeNarc 0.11

This rule detects when the `power(Object)` method is called directly in code instead of using the `**` operator. A groovier way to express this: `a.power(b)` is this: `a ** b`. This rule can be configured to ignore `this.power(Object)` using the ignoreThisReference property. It defaults to false, so even `power(x)` will trigger a violation.

This rule also ignores all calls to `super.power(Object)`.

### ExplicitCallToRightShiftMethod Rule

Since CodeNarc 0.11

This rule detects when the `rightShift(Object)` method is called directly in code instead of using the >> operator. A groovier way to express this: `a.rightShift(b)` is this: `a >> b`. This rule can be configured to ignore `this.rightShift(Object)` using the ignoreThisReference property. It defaults to false, so even `rightShift(x)` will trigger a violation.

This rule also ignores all calls to `super.rightShift(Object)`.

### ExplicitCallToXorMethod Rule

Since CodeNarc 0.11

This rule detects when the `xor(Object)` method is called directly in code instead of using the `^` operator. A groovier way to express this: `a.xor(b)` is this: `a ^ b`. This rule can be configured to ignore `this.xor(Object)` using the ignoreThisReference property. It defaults to false, so even `xor(x)` will trigger a violation.

This rule also ignores all calls to `super.xor(Object)`.

### ExplicitHashMapInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of `HashMap`. In Groovy, it is best to replace `new HashMap()` with `[:]`, which creates (mostly) the same object. `[:]` is technically a LinkedHashMap but it is very rare that someone absolutely needs an instance of `HashMap` and not a subclass.

### ExplicitLinkedHashMapInstantiation Rule

Since in CodeNarc 0.14

This rule checks for the explicit instantiation of a `LinkedHashMap` using the no-arg constructor. In Groovy, it is best to replace `new LinkedHashMap()` with `[:]`, which creates the same object.

### ExplicitHashSetInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of `HashSet`. In Groovy, it is best to replace `new HashSet()` with `[] as Set`, which creates the same object.

### ExplicitLinkedListInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of `LinkedList`. In Groovy, it is best to replace `new LinkedList()` with `[] as Queue`, which creates the same object.

### ExplicitStackInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of `Stack`. In Groovy, it is best to replace `new Stack()` with `[] as Stack`, which creates the same object.

### ExplicitTreeSetInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of `TreeSet`. In Groovy, it is best to replace `new TreeSet()` with `[] as SortedSet`, which creates the same object.

### GetterMethodCouldBeProperty Rule

New in CodeNarc 0.16

If a class defines a `public` method that follows the Java getter notation and that returns a constant, then it is cleaner to provide a Groovy property for the value rather than a Groovy method.

Example of violations:

        interface Parent {
            String getSomething()
            String getSomethingElse()
        }

        class Child extends Parent {
            static VALUE = 'value'

            @Override
            String getSomething() {
                'something'         // this could be simplified
            }

            @Override
            String getSomethingElse() {
                VALUE       // this could be simplified
            }

            int getOtherValue() {
                123
            }

            static String getName() {
                'MyName'
            }
        }

        class Child2 extends Parent {
            static VALUE = 'value'
            final String something = 'something'    // this is cleaner
            final String somethingElse = VALUE      // this is cleaner
            final int otherValue = 123              // this is cleaner
            static final String name = 'MyName'     // this is cleaner
        }

### GroovyLangImmutable Rule

New in CodeNarc 0.13

The `groovy.lang.Immutable` annotation has been deprecated and replaced by `groovy.transform.Immutable`. Do not use the `Immutable` in `groovy.lang`.

Example of violations:

        @Immutable
        class Person { }

        @groovy.lang.Immutable
        class Person { }

        import groovy.lang.Immutable as Imtl
        @Imtl
        class Person { }

        // the following code is OK
        @groovy.transform.Immutable
        class Person { }

        import groovy.transform.Immutable
        @Immutable
        class Person { }

        import groovy.transform.*
        @Immutable
        class Person { }

        import groovy.transform.Immutable as Imtl
        @Imtl
        class Person { }

### GStringAsMapKey Rule

Since CodeNarc 0.11

A GString should not be used as a map key since its hashcode is not guaranteed to be stable. Consider calling `key.toString()`.

Here is an example of code that produces a violation:

        Map map = ["${someRef}" : 'invalid' ]       // violation

### GStringExpressionWithinString Rule

Since CodeNarc 0.19

Check for regular (single quote) strings containing a GString-type expression ($..).

Example of violations:

        def str1 = 'total: ${count}'                // violation
        def str2 = 'average: ${total / count}'      // violation

        def str3 = "abc ${count}"                   // ok; GString
        def str4 = '$123'                           // ok
        def str5 = 'abc {123}'                      // ok

### UseCollectMany Rule

New in CodeNarc 0.16

In many case `collectMany()` yields the same result as `collect.flatten()`. It is easier to understand and more clearly conveys the intent.

Example of violations:

    def l = [1, 2, 3, 4]

    l.collect{ [it, it*2] }.flatten() // suboptimal

    l.collectMany{ [it, it*2] }       // same functionality, better readability

### UseCollectNested Rule

New in CodeNarc 0.16

Instead of nested `collect` calls use `collectNested`.

Example of violations:

    def list = [1, 2, [3, 4, 5, 6], [7]]

    println list.collect { elem ->
        if (elem instanceof List)
            elem.collect {it *2} // violation
        else elem * 2
    }

    println list.collect([8]) {
        if (it instanceof List)
            it.collect {it *2} // violation
        else it * 2
    }

    println list.collectNested { it * 2 } // same functionality, better readability