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[0] https://docs.python.org/3/library/typing.html (from Python 3.5 - released Sep 2015)
[1] https://github.com/python/mypy (v0.1 released Sep 2009)
A quirk of Go is that I can cast a `[]string` to `interface{}`, but I cannot cast `[]string` to `[]interface{}`. This blog post is my go-to explanation for why the second is not possible but the former is.
Earlier quoted context omitted.
Is that really a "quirk" of specifically Go? I am pretty sure Java--the implementation of which defined a lot of how numerous languages handle this kind of thing--has the same behavior: you can cast String[] to Object, but not Object[].
C# allows casting string[] to object[], but this requires the compiler to insert runtime type checks each time the array elements are modified: object[] array = new string[10]; // throws a run-time exception array[0] = 10;
Other data structures like List, Span, etc. do away with covariance. There's an upcast for ReadOnlySpan but only because it's zero-cost and does not introduce the issues stemming from covariance.
Luckily, you almost never see someone use array covariance beyond occasional object[] upcasts (and the compiler is also good at reasoning whether to insert covariance checks or not).
If you are mindful of performance, one thing to be careful of, is that interfaces often prevent inlining and can cause performance issues. Generally speaking the Go compiler seems to have trouble with inlining, PGO (profile guided optimization) can help though.
Storing concrete values into interfaces often cause allocations, which has a larger impact on performance than inlining.
If you are mindful of performance, one thing to be careful of, is that interfaces often prevent inlining and can cause performance issues. Generally speaking the Go compiler seems to have trouble with inlining, PGO (profile guided optimization) can help though.
> Go compiler seems to have trouble with inlining not "have trouble", a deliberate design to keep compile times fast and (emitted) code size reasonable
If you are mindful of performance, one thing to be careful of, is that interfaces often prevent inlining and can cause performance issues. Generally speaking the Go compiler seems to have trouble with inlining, PGO (profile guided optimization) can help though.
Earlier quoted context omitted.
C# allows casting string[] to object[], but this requires the compiler to insert runtime type checks each time the array elements are modified: object[] array = new string[10]; // throws a run-time exception array[0] = 10;
Note that array covariance is largely considered a design mistake and if .NET was to be redone it wouldn't have one (and a bunch of smaller things that are an artifact of generics getting introduced in C# 2.0 and not 1.0, well, the problem is much worse in Go heh). Other data structures like List , Span , etc. do away with covariance. There's an upcast for ReadOnlySpan but only because it's zero-cost and does not int…
Thus having high compatibility with how Java used to be was a big factor designing C# 1.00
A quirk of Go is that I can cast a `[]string` to `interface{}`, but I cannot cast `[]string` to `[]interface{}`. This blog post is my go-to explanation for why the second is not possible but the former is.
> I can cast a `[]string` to `interface{}`, but I cannot cast `[]string` to `[]interface{}` Surely that's just contravariance, though? You can't cast []string to []any because that would allow you to write non-strings to it.
For those who aren't familiar with the issue, in Java you can assign an array of a subclass to a variable declared as an array of the superclass, which leads to issues if you actually try to mutate it. Imagine if Cat and Dog both inherit from Animal, assigning a Dog[] to an Animal[] is totally valid, but then setting one of the elements to a Cat will throw an an exception.
The comparisons to python are a bit dated now. All of the examples can be implemented in python using typing extensions [0] and statically checked before runtime using mypy [1]. [0] https://docs.python.org/3/library/typing.html (from Python 3.5 - released Sep 2015) [1] https://github.com/python/mypy (v0.1 released Sep 2009)
Python was the first language I made money with. However, these days, I struggle to read and make sense of type-ridden, generic-filled, Pydantic-infested Python code.