Difference Between Constant and Readonly

We use the command constant or readonly to apply or denote a constant while writing the program.

However, how are they different and what is the purpose of using them differently if they both have the same task of assigning constants? So, just to be clear, we’ll be discussing the differences between the two.

Constant vs Readonly

The main difference between constant and readonly is that constant is code that is written at compile-time, whereas readonly is code that is written at run time. This means that the constant keyword should be used to define any constant that holds throughout the universe, whereas the readonly keyword should be used to define a constant that only holds during the running time.

Constant vs Readonly

When attempting to define a constant, the constant keyword is used. The distinction is that it is written during the compilation process. As a result, it’s a compile-time constant.

As a result, you write the program, and the compiler converts it to IL code. The intermediate language code is the IL code. The constant you want to define is directly present while the conversion is taking place.

As a result, the constant will remain constant always.

On the other hand, if the program is Readonly, you must first write it but do not need to directly initialize it. You have the option of taking one of two paths.

You can either initialize it at the time you declare the readonly keyword or in the class’s constructor As a result, attempting to initialize it outside of the declaration or constructor will result in an error.

Comparison Table Between Constant and Readonly

Parameters of comparison Constant Readonly 
Definition If you are trying to create a constant field you need to use the constant keyword.For creating a readonly field you require to use the readonly keyword.
Kind It is referred to as the compile-time constantIt is referred to as the run time constant
Can it be defined within a method?Yes No 
Can it be changed after it is declared?No Yes 
Can you use static modifiers with it?No Yes 

What is Constant?

When it comes to developing computer programming, some guidelines must be followed. There are a lot of keywords that are assembled and told how to run a program in the appropriate method.

As a result, understanding the true importance of the phrase is essential before defining the specific term at the exact time.

And there are a variety of terms that appear to have the same apparent meaning when employed in different contexts. We’ll discuss one such term, the constant keyword, in this article.

Knowing the difference between the constant and readonly keywords is essential for a programmer to be able to distinguish between them.

Because the value must be assigned at build time, a constant keyword is referred to as a compile-time constant.

Once you’ve assigned a value, you can’t change it again through programming; otherwise, an error will appear. It is not possible to modify the value once it has been assigned.

By default, a constant is static. There are several different types of numeric and character constants. To avoid errors, values must be assigned at the time of compilation.

You can’t use constant modifiers with constant keywords. The constant keyword is also used for absolute constants or values that are universal constants.

What is Readonly?

We’re concentrating on the important difference between the constant and readonly keywords here. Both are perplexed since they believe they are tasked with assigning a constant in the program.

However, they are not the same and are utilized in distinct ways. The constant keyword and its use have already been discussed. Here are some ways to tell the difference between the two.

When it comes to readonly keywords in computer language, there are four scenarios in which the readonly keyword can be used.

The readonly keyword, unlike constant keywords, is frequently referred to as a run-time constant because it can be declared at run time.

The value can be set in the function constructor, and it is still within the same class. Readonly keywords, unlike constant keywords, can be assigned multiple times in the declaration field or function constructor.

If the function constructor already exists, you can’t assign a readonly field.

As a result, the readonly value types field is immutable; on the other hand, reference types should contain data that is compatible with the subject of the readonly command.

Then there is readonly struct, readonly instance members, and a ref readonly method return. Each field has a different significance. Overall for assigning constants of these kinds one can use the readonly keyword.

Main Differences Between Constant and Readonly

  1. If you want to create a constant field, use the constant keyword, whereas if you want to create a readonly field, use the readonly keyword.
  2. The compile-time constant is known as the constant, whereas the readonly constant is known as the run-time constant.
  3. A constant can be specified within a method, although a readonly cannot.
  4. Once a constant is stated, it cannot be altered, whereas readonly can be declared several times.
  5. Static modifiers cannot be applied to constants, although they can be applied to readonly variables.

Conclusion 

A compile-time constant is referred to as a constant keyword. You can’t change a value you’ve assigned through programming; otherwise, an error would display.

Values must be assigned at the time of compilation to avoid mistakes. Constant modifiers aren’t compatible with constant keywords. The constant keyword is used when attempting to define a constant.

As a result, it’s a constant at compile time.

Because it can be declared at run time, the readonly keyword, unlike constant keywords, is often referred to as a run-time constant.

Readonly keywords can be allocated numerous times in the declaration field or function constructor, unlike constant keywords. You can’t assign a readonly field to a function constructor that already exists.

The major distinction between constant and readonly code is that the former is written at compile-time, whilst the latter is written at run time.

This means that the constant keyword should be used to create any constant that holds throughout the universe, whereas the readonly keyword should be used to describe a constant that only holds while the program is running.

References

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