不使用eval

Question

["if", "2", "<", "4"]

執行在Ruby中的比較我如何串在一起，這些並計算出它們是否是真實的，而不使用.eval()？

爲了便於說明，上面只是一個數組，我需要操縱內容以便評估if 2 < 4，這應該返回true。

Answer 1

您可以嘗試解析您的語句並將其組合成更復雜的東西。

def bool_parse(statement) 
    op, left, method, right = statement 
    left = left.to_i unless left["\'"] 
    right = right.to_i unless right["\'"] 

    case op 
    when "if", "elsif" 
    left.send(method, right) 
    when "unless" 
    !left.send(method, right) 
    end 
end 

def compose(statements) 
    correct = statements.detect do |s, v| 
    bool_parse(s) 
    end 
    correct && correct.last 
end 

compose({["if", "3", ">", "5"] => 1}) 
#=> nil 
compose({["if", "3", ">", "5"] => 1, ["elsif", "2", ">", "-1"] => 2}) 
#=> 2