Runtime evaluation: Difference between revisions

<pre>[2011, 2016, 2022, 2033, 2039, 2044, 2050, 2061, 2067, 2072, 2078, 2089, 2095, 2101, 2107, 2112, 2118]</pre>

 

The '''GroovyShell''' class allows the evaluation of a string or of the text contents of a '''File''' or '''InputStream''' as a ''Groovy script''. A script is a either a set of statements to be executed in order, or a Groovy class with a '''main()''' method, or a Groovy '''Thread''' subclass or '''Runnable''' implementation. The return value is the value of the last statement executed, or the value of an explicit '''return''' statement (if any).

 

The last expression evaluated in the script, a list of years found, is the return value of the '''evaluate()''' method.

 

There are several approaches to evaluating a script with variables:

*'''GString''' embedded values

*'''Eval''' shortcut

 

Setting up the script as a '''GString''' with embedded value parsing is a "natural" ''ad hoc'' solution for Groovy programmers, but there are possible pitfalls if the script itself contains '''GString'''s.

<lang groovy>def startYear = 2008

Notice that in the script the embedded value "${it}" must be ''quoted'' with backslash (\) to prevent parsing as a part of the script '''GString'''. However, it is still correctly parsed within the internal '''GString''' when the script is run.

 

'''GroovyShell''' uses a '''Binding''' object to pass variable values to a script. This is the only way to pass variables if the script comes from a '''File''' or '''InputStream''', but even if the script is a string '''Binding''' avoids the nested quoting issue caused by the ''ad hoc'' use of '''GString'''.

<lang groovy>def context = new Binding()

println binding.yearList</lang>

 

For simple evaluation of string-based scripts with only a few variables (like this one), the '''Eval''' class has static shortcut methods that do the '''Binding''' setup and '''GroovyShell''' evaluation under the surface. '''Eval.me(script)''' evaluates a script with no variables. '''Eval.x(x,script)''', '''Eval.xy(x,y,script)''', or '''Eval.xyz(x,y,z,script)''' each evaluates a script with 1, 2, or 3 variables, respectively. Here is an example with start and end years as script variables ''x'' and ''y''.

<lang groovy>def years5 = Eval.xy(2008, 2121, '''