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I'm confused by the `SuspiciousCollectionReassignment` inspection. The <description> says: ``` fun ...
# stdlib
m
I'm confused by the 
SuspiciousCollectionReassignment
inspection. The description says:
Copy code
fun test() {
      var list = listOf(0)
      list += 42 // new list is created, variable 'list' still contains only '0'
  }
But doing the same thing in playground yields 
[0, 42]
. What am I missing?
p
The wording is a bit confusing, but the reason it’s “suspicious” is that the 
+=
operator is quietly allocating an entire new collection
m
Yea but sometimes you have no control over this
Typically Gradle 
var
properties
p
🤷 it’s “suspicious”, not “wrong”
m
Yup
p
I think the preferred way to work around (rather than a suppress warnings) would be to make it explicit you’re setting to a new list, e.g. 
list = list + 42
👍 1
but there’s also nothing stopping you from suppressing and moving on 🙂
m
I've been suppressing this one for years, don't know why I decided to investigate more today 🙂
K 1
That clears it up, thanks!
👍 1
n
One reason I can see for "suspicious" is that 
var l1 = listOf(0); var l2 = l1; l1 += 42
results in "l2=[0]", but a 
var l1 = mutableListOf(0); var l2 = l1; l1 += 42
results in "l2=[0,42]"
m
It behaves exactly like int: 
var l1 = 0; var l2 = l1; l1 += 42
results in "l2==0" so I'd argue this is behaving as expected
I think the issue is with performance, not behaviour
n
the "MutableList" case behaves differently.
m
Ooo right, I see it now
The fact that 
l1 += 42
is not the same as 
l1 = l1 + 42
in the mutable case feels weird
m
IMO this introspection could trigger just on 
+=
with `var MutableList`but no with `var List`nor 
val MutableList
.
plus one 1
a
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