How to check if an instance is of type String or GString in Groovy

Question

I would like to learn what the robust way of checking, if a variable is of type string or gstring, is. I suppose it is different than in pure Java:

def var = someFunc();

if (var instanceof String || var instanceof GString) {
   String str = var;
}

I ask, because I do not want to be surprised that I have missed a Groovy specific feature that causes a hard to debug bug.

Disappointing there's not a neater way to do this, e.g. var.isString() — Armand, Nov 15 '12 at 09:07

score 44 · Accepted Answer · answered Jun 16 '11 at 21:29

44

Instanceof tests should work:

assert "fasd" instanceof String
assert "${this}" instanceof GString

answered Jun 16 '11 at 21:29

Andrew Eisenberg

28,387
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score 19 · Answer 2 · answered Mar 03 '16 at 11:21

Another way is to use the in keyword:

groovy:000> t = "hello"
===> hello
groovy:000> t in String
===> true
groovy:000> "${t}" in GString
===> true

The in keyword is the membership operator, and gets translated to an isCase call on the class:

groovy:000> String.isCase(t)
===> true
groovy:000> GString.isCase("${t}")
===> true

score 2 · Answer 3 · edited Aug 02 '19 at 00:44

2

You can also use the .class method on a Groovy object

def a = "test"
def b = "${a}"

assert a.class == String
assert b.class == org.codehaus.groovy.runtime.GStringImpl

Note that a GString is easily evaluated and turned into a String, e.g. by calls to toString.

If you're looking for template-like functionality to have re-usable string definitions to pass around and leverage, you should consider the Groovy template engine.

see http://groovy.codehaus.org/Groovy+Templates

edited Aug 02 '19 at 00:44

Sebastian

6,293
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47

answered Jun 19 '11 at 19:41

Al Baker

524
2
3

3

You have to be careful is `a` is a `Map` though, as `a.class` will return `null` – tim_yates Jun 20 '11 at 14:19

How to check if an instance is of type String or GString in Groovy

3 Answers3

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