19.md

LERN/LS/19

This example consists of a single file, LS/19.iss

This example demonstrates the use of a switch to selectively execute one out of several possible code segments, called branches.

Enter the command run lern/ls/19 to run the example.

The switch statement

A switch identifies a branch of code to execute based on a single provided value. The statement itself looks like so:

switch value

A switch is always followed by a block of braces { and }, each on its own line as is the LavishScript way. The switch block is then filled with the possible branches of code to select from.

Switch case

A case statement specifies text to directly compare the value to. The comparison is a case-insensitive string compare. The statement itself looks like so:

case value

• Note: In many languages, a switch case value is numeric and/or followed by a : (colon) as a matter of syntax. LavishScript treats the case value as verbatim text to compare, including any quotes or trailing colon.

If the value matches the switch line's, then code execution will continue immediately following the case statement.

Code execution will then continue downward as usual, including any additional branches below! To skip past the end of the siwtch, use a break statement.

A typical switch pattern with multiple cases can therefore look like this:

switch ${ValueToCheck}
{
    case value
        echo value matched
        break
    case value1
    case value2
        echo value1 or value2 matched
        break
}

Switch default

A default statement is used to specify a default branch to execute if no other branch was found to match the value specified by switch

A typical switch pattern with a default branch can look like this:

switch ${ValueToCheck}
{
    case value1
        break
    case value2
        break
    default
        echo No match!
        break
}

Switch variablecase

A variablecase statement can be used to provide dynamic branch values, which cannot be hard-coded into a typical case statement.

Where a typical case is intended for verbatim comparison, a variablecase is expected to contain one or more Data Sequences that must first be resolved before comparison can be performed.

A variablecase statement therefore typically looks something like this:

variablecase ${Value}

If no case statement matched, then before the default is selected, each specified variablecase is then checked in order from top to bottom.

If a matching variablecase is found, execution continues from below that variablecase, the same way as is done for a case or default. Any further variablecase lines are ignored, and their Data Sequences will not be resolved.

Exercises

1. Add your own branch to the switch by adding a case, an echo, and a break. Run the script again, passing the value you specified on the case line as a parameter.

2. Create your own .iss file with a main function that accepts a string parameter, and a switch to selectively output something different if "On" or "Off" is passed as to the script. Use default to detect that neither matched, and tell the user to provide On or Off!