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Using Literal Values in an Action Invocation

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The action invocation in the RuleAttribute attribute is used to establish the correspondence between the Cord action declaration signature and the potentially different rule method signature. If an action invocation argument is a literal value (for example, a number) it is not mapped to a rule method parameter.

During exploration, the action invocation for the rule is consumed by the Cord interpreter. Spec Explorer explores the rule method only when the action parameter matches the literal value in the action invocation.

Supported Literal Types

The Cord syntax supports the following types of literals as action invocation arguments:

  • Boolean literals, either true or false in C#.

  • Integer literals, such as -5 or 41.

  • Real literals, such as -1 or 5.33.

  • Character literals, such as 'a' or 'B'.

  • String literals, such as "Kim".

  • Null literals, such as (string)null or (Set<int>)null.

  • Modeling collection literals, such as Map<int,char>{1->'a',2->'b'}.

Note

The action invocation for a rule is provided as a string. To specify a string literal in a rule declaration in C#, use the backslash (\) to escape each quotation mark (") around the literal value.

Spec Explorer supports as action parameters the three immutable collection types Map, Set, and Sequence in the Microsoft.Modeling namespace.

Examples

The following examples use conditions to ensure that only one rule is enabled for any given input parameter.

Example 1

The following example declares a GetQualifiedMinimum action in Cord script, and then shows C# rule definitions that model the action. The action returns the minimum value from a set of positive integers, or an error value, if the set is invalid or not supported. In this example, Spec Explorer would examine one of the four rules, based on the value of the input parameter, numbers.

  • If the input parameter is null, Spec Explorer examines the GetQualifiedMinimumNull method and sets the return parameter to -2.

  • If the input parameter is the empty set, Spec Explorer examines the GetQualifiedMinimumEmpty method and sets the return parameter to 0.

  • If the input parameter is a set that contains any non-positive numbers, Spec Explorer examines the GetQualifiedMinimumError method and sets the return parameter to -1.

  • Otherwise, Spec Explorer examines the GetQualifiedMinimum method and sets the return parameter to the return value of the method.

The following Cord script shows the action declaration.

action abstract static int Adapter.GetQualifiedMinimum(Set<int> numbers);

The follow C# code shows corresponding rule definitions.

[Rule(Action = "GetQualifiedMinimum((Set<int>)null) / -2")]
static void GetQualifiedMinimumNull() { }

[Rule(Action = "GetQualifiedMinimum(Set<int>{}) / 0")]
static void GetQualifiedMinimumEmpty() { }

[Rule(Action = "GetQualifiedMinimum(numbers) / -1")]
static void GetQualifiedMinimumError(Set<int> numbers)
{
    Condition.IsNotNull(numbers);
    Condition.Exists(numbers, n => n <= 0);
}

[Rule(Action = "GetQualifiedMinimum(numbers) / result")]
static int GetQualifiedMinimum(Set<int> numbers)
{
    Condition.IsNotNull(numbers);
    Condition.IsTrue(numbers.Count > 0);
    Condition.All(numbers, n => n > 0);
    return numbers.Min();
}

Example 2

The following example declares a GetFirstCharacterAndLength action in Cord script, and then shows C# rule definitions that model the action. The action returns the first character of a string and also sets an output parameter to the input string's length. In this example, Spec Explorer would examine one of the three rules, based on the value of the input parameter, name.

  • If the input parameter is null, Spec Explorer examines the GetFirstCharacterAndLengthForNull method and sets the return parameter to null and the output parameter to -1.

  • If the input parameter is the empty string, Spec Explorer examines the GetFirstCharacterAndLengthForEmpty method and sets the return parameter to null and the output parameter to 0.

  • Otherwise, Spec Explorer examines the GetFirstCharacterAndLength method.

The following Cord script shows the action declaration.

action abstract static string Adapter.GetFirstCharacterAndLength(string name, out int length);

The follow C# code shows corresponding rule definitions.

[Rule(Action = "GetFirstCharacterAndLength((string)null , out -1) / (string)null")]
static void GetFirstCharacterAndLengthForNull() { }

[Rule(Action = "GetFirstCharacterAndLength(\"\", out 0) / (string)null")]
static void GetFirstCharacterAndLengthForEmpty() { }

[Rule(Action = "GetFirstCharacterAndLength(name, out length) / result")]
static string GetFirstCharacterAndLength(string name, out int length)
{
    Condition.IsNotNull(name);
    Condition.IsTrue(name.Length > 0);
    length = name.Length;
    return name.Substring(0, 1);
}

Example 3

The following example declares a GetFirstName action in Cord script, and then shows C# rule definitions that model the action. The action returns the first name from a sequence of names. In this example, Spec Explorer would examine one of the three rules, based on the value of the input parameter, names.

  • If the input parameter is null, Spec Explorer examines the GetFirstNameNull method and sets the return parameter to null.

  • If the input parameter is the empty sequence, Spec Explorer examines the GetFirstNameEmpty method and sets the return parameter to null.

  • Otherwise, Spec Explorer examines the GetFirstName method.

The following Cord script shows the action declaration.

action abstract static string Adapter.GetFirstName(Sequence<string> names);

The follow C# code shows corresponding rule definitions.

[Rule(Action = "GetFirstName((Sequence<string>)null)/ (string)null")]
static void GetFirstNameNull() { }

[Rule(Action = "GetFirstName(Sequence<string>{})/ (string)null")]
static void GetFirstNameEmpty() { }

[Rule(Action = "GetFirstName(names)/ result")]
static string GetFirstName(Sequence<string> names)
{
    Condition.IsNotNull(names);
    Condition.IsTrue(names.Count > 0);
    return names[0];
}

Example 4

The following example declares a GetAbsoluteValue action in Cord script, and then shows C# rule definitions that model the action. The action returns the absolute value of the input value. In this example, Spec Explorer would examine one of the two rules, based on the value of the input parameter, number.

  • If the input parameter is a non-negative value, Spec Explorer examines the GetAbsoluteValuePos method and sets the return parameter to the input parameter.

  • If the input parameter is a negative value, Spec Explorer examines the GetAbsoluteValueNeg method and sets the return parameter to the method's return value.

The following Cord script shows the action declaration.

action abstract static int Adapter.GetAbsoluteValue(int number);

The follow C# code shows corresponding rule definitions.

[Rule(Action = "GetAbsoluteValue(number) / number")]
static void GetAbsoluteValuePos(int number)
{
    Condition.IsTrue(number >= 0);
}

[Rule(Action = "GetAbsoluteValue(number) / result")]
static int GetAbsoluteValueNeg(int number)
{
    Condition.IsTrue(number < 0);
    return -number;
}

See Also

Reference

RuleAttribute

Concepts

Rules
Rule Attribute