Crystal: BUG: Hash merge ambiguous call matches both Int8 and Int16

[stepanvanzuriak]

I get this error while trying update Hash using old value with merge!

My code:

# Error in line 2: instantiating '(Int32 | String)#+(Int32)'
# in line 2: ambiguous call matches both Int8 and Int16

data = {"name" => "user", "age" => 12}
puts data.merge!({"age" => data["age"] + 2})

But this works great:

data = {"name" => "user", "age" => 12}
puts data.merge!({"age" => 13})
puts data.merge!({"age" => 12 + 2})

Playground example:
https://play.crystal-lang.org/#/r/4t4o

[asterite]

data["age"] can either by a String or an Int32, so that + won't work.

Of course you as the programmer who wrote the code knows that data["age"] is an Int32, but the compiler has no idea, it just sees that you are accessing some element in the Hash.

You can do data["age"].as(Int32) to solve this.

Or probably not use a Hash at all and use classes if you can.

[stepanvanzuriak]

Thanks for explanation

[straight-shoota]

But that error message ambiguous call matches both Int8 and Int16 looks strange.

[asterite]

Hm, right. You can reproduce that with:

a = 1 || "foo"
a + 2

[asterite]

but I'd open that as a separate issue

[stepanvanzuriak]

Works fine with NamedTuple

data = {name: "user", age: 12}
puts data.merge({age: data[:age] + 4})

https://play.crystal-lang.org/#/r/4t7x

[NIFR91]

@stepanvanzuriak because the types of each key in NamedTuple are known at compile time.

The hash is a mutable object , for example:

data = { :name => "user", :age => 12} #=> Hash(Symbol, Int32 | String)
data[:name] = 12 
data[:age] = "old" 
data # => {:name => 12, :age => "old"}

but the NamedTuple is a inmutable struct, but the type of each key is known by the compiler so it knows
data[:age] is a Int32, so it can respond to :+

data = {name: "user", age: 12} #=> NamedTuple(name: String, age: Int32)

From the docs

The compiler knows what types are in each key, so when indexing a named tuple with a symbol literal the compiler will return the value for that key and with the expected type