How to use union in "if" statement [Crystal] -

following code works , print "5.0"

$x : float64 $y : float64 $x = 3.0_f64 $y = 2.0_f64 puts $x + $y 

now, change code support "nil".

$x : float64? $y : float64? $x = 3.0_f64 $y = 2.0_f64 puts $x + $y if !$x.nil? && !$y.nil? 

however code reports following error message.

 no overload matches 'float64#+' type (float64 | nil) overloads are:  - float64#+(other : int8)  - float64#+(other : int16)  - float64#+(other : int32)  - float64#+(other : int64)  - float64#+(other : uint8)  - float64#+(other : uint16)  - float64#+(other : uint32)  - float64#+(other : uint64)  - float64#+(other : float32)  - float64#+(other : float64)  - number#+() couldn't find overloads these types:  - float64#+(nil)      puts $x + $y if !$x.nil? && !$y.nil? 

i stop call of method "#+()" if $x or $y nil , print calculated result if both float64.

what best practice situation?

---

in above code, simplified code question. in result, meaning of question changed involuntarily.. wanted ask following code actually.

class xyz   property a, b   @a : float64?   @b : float64?    def initialize     @a = nil     @b = nil   end    def do_calc     if !@a.nil? && !@b.nil?       puts @a + @b     else       puts "we can't calculate because '@a or @b has nil."     end   end end  x = xyz.new x.a = 3.0_f64 x.b = 2.0_f64 x.do_calc 

this code, reports following error.

 instantiating 'xyz#do_calc()'  x.do_calc   ^~~~~~~  in ./a.cr:15: no overload matches 'float64#+' type (float64 | nil) overloads are:  - float64#+(other : int8)  - float64#+(other : int16)  - float64#+(other : int32)  - float64#+(other : int64)  - float64#+(other : uint8)  - float64#+(other : uint16)  - float64#+(other : uint32)  - float64#+(other : uint64)  - float64#+(other : float32)  - float64#+(other : float64)  - number#+() couldn't find overloads these types:  - float64#+(nil)        puts @a + @b 

how can avoid error?

be sure read docs if, , checking nil: https://crystal-lang.org/docs/syntax_and_semantics/if_var.html , https://crystal-lang.org/docs/syntax_and_semantics/if_var_nil.html

this applies local variables, you'll need assign values local variables first.

as side note, global variables don't exist anymore in language of crystal 0.19.0.