Abstract
- A set of Instruction that can be triggered to accomplish a particular task
Function Signature
- Refers to the declaration of a function
- The signature is the combination of the function’s name, argument types, argument order, argument count, and return type
Java function signature and function descriptor
In Java, the return type isn’t part of the function signature. The method signature is the combination of the method name and the parameter list (argument types, argument order and argument count).
The method descriptor of Java is made of the function signature and the return type.
Function Scope Rule
- Local parameters and variables are only accessible within the function they are declared in
In C, what if I have a local variable and a global variable with the same name?
C will prioritize the local variable within its scope.
Function Call
- When a function is called, an activation record is created on the call stack, allocating memory for its local parameters and variables. Once the function completes, its activation record is removed, and the allocated memory is released. Thus, local parameters and variables exist in memory only during the function’s execution and are known as automatic variables. In contrast, static variables persist in memory even after the function’s execution.
Passing by value to a new function call
The new function receives its own set of automatic variables and operates on them, not the automatic variables of the calling function.
First-class Citizen Function
- Function that can be manipulated and used in flexible ways like a variable. This is what powers Higher-order Function
Behave and treated like a variable
- Assigned to variables
- Passed as arguments to other functions
- A function can be the return value of another function
- Can store functions in data structures like Array, List, or Hash Map etc
This enables powerful programming techniques like Higher-order Function and Closure etc.
Important
There isn’t first class citizen function in Java, Java creates an illusion of it using Java Lambda & Functional Interface.
Higher-order Function
- A Function that takes in another one or more functions as inputs or return a function as its output
Important
Higher-order function builds on top of First-class Citizen Function, so we can pass function into another function or return function from another function as if function is a variable.
Higher-order function powers Closure.
Common higher-order functions
map(): take in a function, and uses it to implement changes on a stream of values.
filter(): take in a function, and uses it to remove some values from a stream of values.
reduce(): takes in a function, and uses it to convert a stream of values into a single value.
Rust Function
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For Function Signature, you must declare the Datatype of each parameter
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So Compiler almost never needs you to use the function elsewhere in the code to figure out what type you mean. The compiler is also able to give more helpful error messages if it knows what types the function expects.
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Return the last Expression implicitly