Update list filter to handle arrays properly (#1013) #1014
Conversation
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@mattcoley, @tkindy |
| @@ -45,6 +47,34 @@ public Object filter(Object var, JinjavaInterpreter interpreter, String... args) | |||
| result = Chars.asList(((String) var).toCharArray()); | |||
| } else if (Collection.class.isAssignableFrom(var.getClass())) { | |||
| result = Lists.newArrayList((Collection<?>) var); | |||
| } else if (var.getClass().isArray()) { | |||
| if (var instanceof boolean[]) { | |||
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I was looking at this last week and couldn't think of a way in Java to handle these primitive arrays generically other than what you did here to list out all the primitive cases. @tkindy curious if you know of a better way to handle this?
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Unfortunately, there is no better way to do that. Most of the other opportunities ends in a list which contains only 1 element, an array. Which is not what we want here. We want to have a list of "n" elements, where the elements coming from an array which length is "n".
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I believe egyedt's correct. As far as I know, there isn't a generic way to handle primitive arrays; like individual primitives, the element type is significant because primitives have different sizes in memory and the type determines how interactions with them are compiled. This contrasts with generic objects like List<T> which only hold references, all of which are the same size in memory.
It seems egyedt is also correct that we need to manually box the primitive arrays before passing to Arrays.asList. Calling Arrays.asList((boolean[]) var) results in a List<boolean[]> rather than a List<Boolean> as we want. This is presumably because Arrays.asList's parameter is typed as T..., where T is inherently a reference type. This clashes with the primitive type of the elements in the array, so the call is resolved as being passed one boolean[] (a reference type) parameter instead of N boolean (a primitive type) parameters.
So I think this is the best we can do. 👍
| @@ -45,6 +47,34 @@ public Object filter(Object var, JinjavaInterpreter interpreter, String... args) | |||
| result = Chars.asList(((String) var).toCharArray()); | |||
| } else if (Collection.class.isAssignableFrom(var.getClass())) { | |||
| result = Lists.newArrayList((Collection<?>) var); | |||
| } else if (var.getClass().isArray()) { | |||
| if (var instanceof boolean[]) { | |||
There was a problem hiding this comment.
I believe egyedt's correct. As far as I know, there isn't a generic way to handle primitive arrays; like individual primitives, the element type is significant because primitives have different sizes in memory and the type determines how interactions with them are compiled. This contrasts with generic objects like List<T> which only hold references, all of which are the same size in memory.
It seems egyedt is also correct that we need to manually box the primitive arrays before passing to Arrays.asList. Calling Arrays.asList((boolean[]) var) results in a List<boolean[]> rather than a List<Boolean> as we want. This is presumably because Arrays.asList's parameter is typed as T..., where T is inherently a reference type. This clashes with the primitive type of the elements in the array, so the call is resolved as being passed one boolean[] (a reference type) parameter instead of N boolean (a primitive type) parameters.
So I think this is the best we can do. 👍
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#1013