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Not really, as there isn't a single way to do what you want. I.e. insert versus update
Plus the table should already be created, that would be out of scope
If it also handled migrations and such
Perhaps a dumb question, but is there any best practice as to when to use
x, @x, or self.x to refer to an instance variable in an instance method? I seem to be able to use all 3 with the same effect.
My guess is that
@x is the only "safe" thing that will always resolve to an ivar, even if there is another local var or method named x...so is there no reason to use the other 2, other than to make things less explicit and confusing? :)
"self.x" is a method (you are probably using the macro "getter") that returns "@x"
and "@x" is the actual instance var
so the best practice if you want to access to the instance var is to use the instance var "@x" :)
<hightower2> sometimes I wish that instead of making local vars be unprefixed, the lang designers chose to prefix local vars... so then the scope/lookup of all unprefixed vars like 'x' or 'var1' would be very uniform regardless of whether it was a property or method
<hightower2> well, I guess if one really wanted to do so, one could stick to a rule of always prefixing local vars with something, manually...
this way its always clear what is a method call and what isnt
however, a good usecase for using
self.x is if you have customer logic in the getter and/or are using a lazily initialized ivar
Oh, glossed over. lazy was already mentioned
Does crystal have anything like...I'm not sure what it's called, but in Nim, you can assign a slice to a slice of a variable...like:
var x = [1, 2, 3, 4, 5]
var y = [6, 7, 8, 9, 10]
x[1..2] = y[1..2] # x => [1, 7, 8, 4, 5]
Oh nice. It seems you can even grow shrink it with unsymmetrical ranges
Thanks @asterite
Yes :-) It's documented here: https://crystal-lang.org/api/1.1.0/Array.html#[]=(range:Range,values:Array(T))-instance-method
Are there functions for extracting the sign and fractional components of floating-point numbers? In some languages you have something like
sign and fract:sign(42.0) # 1.0
sign (-42.0) # -1.0
sign (0.0) # 0.0
fract(42.123) # 0.123
I suppose line 3 can be implemented differently if there is a distinction between IEEE-754 positive and negative zero
last one could just be like
value - (value.floor) probably?
If I have a type with value types (floats) for ivars, is it conventional to call a method which copies it
clone or dup? In this case there is nothing to traverse for a deep copy, but I see some projects use clone in this case, while others use dup, so I'm not sure if there is a consensus.
Maybe I worded it poorly. I was stating that either would be semantically correct for this particular example, and asking if there was a general agreement of which takes preference.
the real use case is to parse a
scope.yml having the properties roots, paths, etc. in a Scope class, I'd like to avoid flow control to check the filters as scope.roots, scope.paths, to something like scope.filters having their own class
I have
Scope with property roots and property paths to pull the data from the file, but what I want when creating the instance is more something like a property filters doing when having roots keys, Root.new(value), etc.
so when filtering, I can just do
scope.filters.all? { |filter| filter.evaluate_with(path) }