Functional Programming - Records



A record is a data structure for storing a fixed number of elements. It is similar to a structure in C language. At the time of compilation, its expressions are translated to tuple expressions.

How to create a record?

The keyword record is used to create records specified with record name and its fields. Its syntax is as follows −

record(recodname, {field1, field2, . . fieldn})

The syntax to insert values into the record is −

#recordname {fieldName1 = value1, fieldName2 = value2 .. fieldNamen = valuen}

Program to create records using Erlang

In the following example, we have created a record of name student having two fields, i.e., sname and sid.

-module(helloworld). -export([start/0]). -record(student, {sname = "", sid}). start() -> S = #student{sname = "Sachin",sid = 5}.

Program to create records using C++

The following example shows how to create records using C++, which is an object-oriented programming language −

#include<iostream> #include<string> using namespace std; class student { public: string sname; int sid; 15 }; int main() { student S; S.sname = "Sachin"; S.sid = 5; return 0; }

Program to access record values using Erlang

The following program shows how access record values using Erlang, which is a functional programming language −

-module(helloworld). -export([start/0]). -record(student, {sname = "", sid}). start() -> S = #student{sname = "Sachin",sid = 5}, io:fwrite("~p~n",[S#student.sid]), io:fwrite("~p~n",[S#student.sname]).

It will produce the following output −

5 
"Sachin"

Program to access record values using C++

The following program shows how to access record values using C++ −

#include<iostream> #include<string> using namespace std; class student { public: string sname; int sid; }; int main() { student S; S.sname = "Sachin"; S.sid = 5; cout<<S.sid<<"\n"<<S.sname; return 0; }

It will produce the following output −

5 
Sachin 

The record values can be updated by changing the value to a particular field and then assigning that record to a new variable name. Take a look at the following two examples to understand how it is done using object-oriented and functional programming languages.

Program to update record values using Erlang

The following program shows how to update record values using Erlang −

-module(helloworld). -export([start/0]). -record(student, {sname = "", sid}). start() -> S = #student{sname = "Sachin",sid = 5}, S1 = S#student{sname = "Jonny"}, io:fwrite("~p~n",[S1#student.sid]), io:fwrite("~p~n",[S1#student.sname]).

It will produce the following output −

5
"Jonny" 

Program to update record values using C++

The following program shows how to update record values using C++ −

#include<iostream> #include<string> using namespace std; class student { public: string sname; int sid; }; int main() { student S; S.sname = "Jonny"; S.sid = 5; cout<<S.sname<<"\n"<<S.sid; cout<<"\n"<< "value after updating"<<"\n"; S.sid = 10; cout<<S.sname<<"\n"<<S.sid; return 0; }

It will produce the following output −

Jonny 
5 
value after updating 
Jonny 
10 
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