Odd behaviour with Map in Groovy

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I was writing code and I noticed some odd behavior in Groovy when I am dealing with XML and Maps. I thought about it and can\'t figure out why is it happening and should it

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迷失自我

2020-12-19 13:51

One thing that might help is, don't use GStrings for your keys. Groovy supports using objects directly as keys by wrapping them in parentheses.

From the manual:

Map keys are strings by default: [a:1] is equivalent to ["a":1]. But if you really want a variable to become the key, you have to wrap it between parentheses: [(a):1].

Fully working example:

def xml = '<xml><head>headHere</head><body>bodyHere</body></xml>'

Map map1 = [:]
def node = new XmlParser().parseText(xml)
node.each {
    map1 << [ (it.name()): it.value() ]
}

println map1
println map1["head"]
println ">>>>>>>>>>>>>>>>>>>>>>"

Map map2 = [:]

map2 << ["head":"headHere"]
map2 << ["body":"bodyHere"]

println map2
println map2["head"]

println "<<<<<<<<<<<<<<<<<<<<<<"

def xml2 = '<xml><head>headHere</head><body>bodyHere</body></xml>'

Map map3 = [:]

def node2 = new XmlParser().parseText(xml2)

node2.each {
    map3[it.name()] = it.value()
}

println map3
println map3["head"]

The output is:

[head:[headHere], body:[bodyHere]]
[headHere]
>>>>>>>>>>>>>>>>>>>>>>
[head:headHere, body:bodyHere]
headHere
<<<<<<<<<<<<<<<<<<<<<<
[head:[headHere], body:[bodyHere]]
[headHere]

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死守一世寂寞

2020-12-19 14:02

Here is a demonstration of this quirk of double quoted strings in Groovy:

Double quoted strings are plain java.lang.String if there’s no interpolated expression, but are groovy.lang.GString instances if interpolation is present.

groovy:000> m = [:]
===> {}
groovy:000> tmp = "wat"
===> wat
groovy:000> key = "${tmp}"
===> wat
groovy:000> m << ["${key}": "hi"]
===> {wat=hi}
groovy:000> m["${key}"] = "hi"
===> hi
groovy:000> m
===> {wat=hi, wat=hi}
groovy:000> m["wat"] = "fuuuuuu!"
===> fuuuuuu!
groovy:000> m
===> {wat=hi, wat=fuuuuuu!}
groovy:000> m.keySet().each { println it.class }
class org.codehaus.groovy.runtime.GStringImpl
class java.lang.String

Enjoy ;)

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