Type Assertions in TypeScript

This blog post is about type assertions in TypeScript, which are related to type casts in other languages and performed via the as operator.

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Table of contents:

• Type assertions
  • Alternative syntax for type assertions
  • Example: asserting an interface
  • Example: asserting an index signature
• Constructs related to type assertions
  • Non-nullish assertion operator (postfix !)
  • Definite assignment assertions

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Type assertions

A type assertion lets us override a static type that TypeScript has computed for a storage location. That is useful for working around limitations of the type system.

Type assertions are related to type casts in other languages, but they don’t throw exceptions and don’t do anything at runtime (they do perform a few minimal checks statically).

const data: object = ['a', 'b', 'c']; // (A)

// @ts-ignore: Property 'length' does not exist on type 'object'.
data.length; // (B)

assert.equal(
  (data as Array<string>).length, 3); // (C)

• In line A, we widen the type of the Array to object.
• In line B, we see that this type doesn’t let us access any properties.
• In line C, we use a type assertion (the operator as) to tell TypeScript that data is an Array. Now we can access property .length.

#typescript #javascript

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What is Assertion in Java? How to use Assertion in Java

Table of Contents

• What is Assertion in Java?
• Syntax
• How to Use Assertion in Java?
• Why Use Assertions?
• Where to use Assertions?
• How to Disable Assertions?
• Ways to use Assertion in Java
• Conclusion

What is Assertion in Java?

The assertion in Java is used to ensure the correctness of any program’s assumptions as the assertion is assumed to be true when it is executed. The Java Virtual Machine throws an error named AssertionError if the assertion is false. The assertion in Java has found its application mainly for testing purposes. Boolean expressions are used along with assertion statements. An assertion is a statement, and the ‘asset’ keyword is used to carry out an assertion in Java.

#full stack development #assertion in java #assertion in java #assertion in java #what is assertion in java #how to use assertion in java

What Is The Main Difference Of TYPES Vs INTERFACES in TypeScript

TypeScript has two ways of declaring structures of your objects in the form of  #types (type aliases) and #interfaces.

In this lesson we will look at the technical differences between these two, when you should use which, along with real world #TypeScript code analysis, and community thoughts

#typescript 

Basic Data Types in Python | Python Web Development For Beginners

At the end of 2019, Python is one of the fastest-growing programming languages. More than 10% of developers have opted for Python development.

In the programming world, Data types play an important role. Each Variable is stored in different data types and responsible for various functions. Python had two different objects, and They are mutable and immutable objects.

Table of Contents  hide

I Mutable objects

II Immutable objects

III Built-in data types in Python

Mutable objects

The Size and declared value and its sequence of the object can able to be modified called mutable objects.

Mutable Data Types are list, dict, set, byte array

Immutable objects

The Size and declared value and its sequence of the object can able to be modified.

Immutable data types are int, float, complex, String, tuples, bytes, and frozen sets.

id() and type() is used to know the Identity and data type of the object

a**=25+**85j

type**(a)**

output**:<class’complex’>**

b**={1:10,2:“Pinky”****}**

id**(b)**

output**:**238989244168

Built-in data types in Python

a**=str(“Hello python world”)****#str**

b**=int(18)****#int**

c**=float(20482.5)****#float**

d**=complex(5+85j)****#complex**

e**=list((“python”,“fast”,“growing”,“in”,2018))****#list**

f**=tuple((“python”,“easy”,“learning”))****#tuple**

g**=range(10)****#range**

h**=dict(name=“Vidu”,age=36)****#dict**

i**=set((“python”,“fast”,“growing”,“in”,2018))****#set**

j**=frozenset((“python”,“fast”,“growing”,“in”,2018))****#frozenset**

k**=bool(18)****#bool**

l**=bytes(8)****#bytes**

m**=bytearray(8)****#bytearray**

n**=memoryview(bytes(18))****#memoryview**

Numbers (int,Float,Complex)

Numbers are stored in numeric Types. when a number is assigned to a variable, Python creates Number objects.

#signed interger

age**=**18

print**(age)**

Output**:**18

Python supports 3 types of numeric data.

int (signed integers like 20, 2, 225, etc.)

float (float is used to store floating-point numbers like 9.8, 3.1444, 89.52, etc.)

complex (complex numbers like 8.94j, 4.0 + 7.3j, etc.)

A complex number contains an ordered pair, i.e., a + ib where a and b denote the real and imaginary parts respectively).

String

The string can be represented as the sequence of characters in the quotation marks. In python, to define strings we can use single, double, or triple quotes.

# String Handling

‘Hello Python’

#single (') Quoted String

“Hello Python”

# Double (") Quoted String

“”“Hello Python”“”

‘’‘Hello Python’‘’

# triple (‘’') (“”") Quoted String

In python, string handling is a straightforward task, and python provides various built-in functions and operators for representing strings.

The operator “+” is used to concatenate strings and “*” is used to repeat the string.

“Hello”+“python”

output**:****‘Hello python’**

"python "*****2

'Output : Python python ’

#python web development #data types in python #list of all python data types #python data types #python datatypes #python types #python variable type

Nominal typing in Typescript

Nominal & structural typing

Type systems are typically categorized as either structural or nominal. Languages like Java and Scala have primarily nominal type systems, whereas a language like Typescript has a structural type system. Let’s take a brief look at both systems.

Nominal Typing

In a nominal typing system, type compatibility is checked using the name of the types. If they do not have the same name, then they are not compatible; end of story. **If **Typescript had a nominal typing system the type check for the last line would fail:

Structural typing

Typescript uses structural typing to decide whether two types are compatible with one another or not. What do we mean by structural typing? Well, let’s consider the following code snippet:

To determine whether the type of the constant color(RGBA) is compatible with the type of serializeColor’s parameter x(RGB) the type system must verify that each member of RGB has a corresponding compatible member in RGBA. In this case, RGB has a single member color for which RGBA has a corresponding member with the same type — [number, number, number] — and so it passes the type check. Notice how the type system ignores the additional members that exist on RGBA (alpha).

#typescript #type-safe #type-systems