Regarding scoping rules this used to trip me up a bit: Python: >>> try: ... x = 2 ... except: ... pass ... >>> x 2 Julia: julia> try x = 2 catch end 2 julia> x ERROR: UndefVarError: `x` not defined

[image] mihalybaci: function foo() try x=2 catch end end foo() #properly returns 2 The equivalent to the REPL example would be as follows. julia> function foo() try x=2 catch end return x end foo (generic function with 1 metho…

I was playing around with it a bit too, and here’s one I don’t quite get. function bar() try x=2 catch end x += 1 return x ends bar() # returns 3 Somehow the += operator is able to grab the value of x when return can’t, then assign to x in a way that can be returned. …

Huh, that is weird. Could that be a bug? This fails (as I would expect it to): julia> function bar() try x = 2 catch end y = x + 1 y end bar (generic function with 1 method) julia> bar() ERROR: UndefVarError: `x` not defi…

x += 1 is x = x + 1. By assigning to x in the outer scope (anywhere, either syntactically before or after the try scope), you’re establishing x as a local name avaliable in bar() — and then the x in the try loop is the same x. Honestly, I think Julia’s scoping behaviors are quite prone to establis…

[image] mbauman: (anywhere, either syntactically before or after the try scope) You need to make it bold - best the “anywhere” a font size larger … and or also after a font larger … to make the point apparent at the first glance. The issue with the mental model is that it usually thinks in te…

[image] mbauman: x += 1 is x = x + 1. By assigning to x in the outer scope (anywhere, either syntactically before or after the try scope), you’re establishing x as a local name avaliable in bar() — and then the x in the try loop is the same x. This is really hard to grasp … I suggest to find …

The set of local names available isn’t imperatively defined/updated by a sequence of events that are executed, but rather it’s a static property of the given scope. Each scope has a concrete set of local names it can use. Those names are established by the assignments that occur in that scope (or …

Scoping rules are probably the thing about Julia I dislike most. In Python you can summarize the rules with “only functions introduce a scope”, which is a simple rule you could get tattooed. In Julia, the rule is more like “Most blocks introduce a scope, but not if a variable is used already local …

[image] mihalybaci: function bar() try x=2 catch end x += 1 return x ends bar() # returns 3 This does seem weird. Stylistically, I think I would always write this as follows even if this is technically unnecessary. function bar() x = 0 try x = 2…

[image] mkitti: function bar() x = 0 try x = 2 catch end x += 1 return x end Or use local to “declare” the variable, which perhaps communicates the intent more clearly: function bar() local x try x = 2 catch end x += 1 return x …

Confusion about scope in try-catch blocks

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Confusion about scope in try-catch blocks

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