ruby dynamic constant assignment error

Dynamic constant assignment – Ruby

Quick Fix: To change the value of a constant in a method, you can use the #replace method for String or Array constants. This allows the object to take on a new value without actually changing the object itself.

The Solutions:

Solution 1:.

In Ruby, constants are meant to be immutable and remain unchanged throughout the program. However, when you assign a new value to a constant within a method, it’s considered a dynamic constant assignment, which is not allowed.

The problem is that each time you run the method, you create a new string object and assign it to the constant. This makes the constant non-constant because its value can change. Even though the contents of the string remain the same, the string object itself is different each time the method is called.

To resolve this issue, consider using an instance variable instead. Instance variables are associated with an instance of a class and can be changed within methods. Here’s an example:

class MyClass def initialize @my_constant = "blah" end

def my_method @my_constant = "new value" end end

In this case, `@my_constant` is an instance variable, and its value can be changed within the `my_method` method. However, the constant `MYCONSTANT` remains unchanged.

Alternatively, if you genuinely want to change the value of a constant within a method, you can use the `#replace` method for String or Array constants. The `#replace` method allows you to modify the contents of the object without changing the object itself.

class MyClass BAR = "blah"

def cheat(new_bar) BAR.replace new_bar end end

Using `#replace`, you can change the value of the constant `BAR` within the `cheat` method without creating a new string object.

Solution 2: Using const_set to Assign Constants Dynamically

Dynamically assigning constants inside methods is discouraged in Ruby, as constants are meant to be immutable. However, if you genuinely need to do this, you can use the `const_set` method.

Here’s an example:

The `const_set` method takes two arguments: the name of the constant as a symbol, and the value you want to assign to it. In this example, we’re assigning the string “foo” to the constant `MY_CONSTANT`. After calling `my_method`, you can access the constant using `MyClass::MY_CONSTANT`.

However, using `const_set` is not recommended for regular use. Consider using class variables, class attributes, or instance variables instead, depending on your specific needs.

Solution 3: Static constant assignment vs dynamic constant assignment

In Ruby, variables assigned with an uppercase are called constants. Another difference between variables and constants is that variables can be dynamically assigned, while constants can only be assigned once. This is because constants are statically defined, meaning their value remains consistent throughout the running program, while variables can change their values during runtime. Therefore, a dynamic constant assignment error occurs when attempting to reassign a constant that has already been assigned a value.

To resolve this issue, there are two common approaches:

• Declare the constant outside of the method :

In this case, "MY_CONSTANT" is declared outside the "my_method" method, making it a statically assigned constant that can be accessed within the method.

• Use a variable :

By declaring "my_local_variable" in the method, it becomes a regular variable that can be dynamically assigned and used within the method.

These approaches ensure that you avoid dynamic constant assignment errors and maintain the integrity of your program’s constants.

Solution 4: Dynamic assignment is not allowed

In Ruby, it is not allowed to define constants inside a method. Constants should be defined outside methods, at the top level or nested inside a module or class.

The error message, “dynamic constant assignment error,” means that you cannot assign a value to a constant in a dynamic way. In other words, you cannot change the value of a constant after it has been defined.

In your example, you are trying to assign the string “blah” to the constant MYCONSTANT inside the mymethod method. This is not allowed because MYCONSTANT is a constant and therefore its value cannot be changed.

Solution 5: Dynamic Constant Assignment

In Ruby, variables are created by assigning them values using the `=` operator. If the variable name starts with a capital letter, it is considered a constant. Constants are meant to be immutable, meaning their values cannot be changed. Trying to assign a new value to a constant results in a “dynamic constant assignment error.”

The code you provided assigns a string value to the variable `MYCONSTANT` inside the `mymethod` method of the `MyClass` class. Since the variable name starts with capital letters, Ruby interprets it as a constant. Attempting to change the constant’s value later in the code would cause the error.

To fix this issue, you can use lowercase letters for the variable name, indicating that it is a regular variable. Here’s an example:

Now, `myconstant` is a regular variable, and you can assign different values to it without encountering the “dynamic constant assignment error.”

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Dynamic constant assignment using non-ascii variable #2079

djberg96 commented Aug 26, 2020

eregon commented Aug 27, 2020

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