In most programming languages strings are immutable. It means that an existing string can't be modified, only a new string can be created out of them.

In Ruby, by default strings are not immutable. To make them immutable, freeze method can be used.

Ruby strings can be compared with three operators:

• With == operator : Returns true or false
• With eql? Operator : Returns true or false
• With casecmp method : Returns 0 if matched or 1 if not matched

Ruby arrays are ordered collections of objects. They can hold objects like integer, number, hash, string, symbol or any other array.

Its indexing starts with 0. The negative index starts with -1 from the end of the array. For example, -1 indicates last element of the array and 0 indicates first element of the array.

A Ruby array is created in many ways.

• Using literal constructor []
• Using new class method

Ruby array elements can be accessed using #[] method. You can pass one or more than one arguments or even a range of arguments.

Syntax:

Ruby array elements can be added in different ways.

• push or
• unshift
• insert

Ruby array elements can be removed in different ways.

• pop
• shift
• delete
• unique

A Ruby hash is a collection of unique keys and their values. They are similar to arrays but array use integer as an index and hash use any object type. They are also called associative arrays, dictionaries or maps.

If a hash is accessed with a key that does not exist, the method will return nil.

A new Time instance can be created with ::new. This will use your current system's time. Parts of time like year, month, day, hour, minute, etc can also be passed.

While creating a new time instance, you need to pass at least a year. If only year is passed, then time will default to January 1 of that year at 00:00:00 with current system time zone.

Ruby range represents a set of values with a beginning and an end. They can be constructed using s..e and s...e literals or with ::new.

The ranges which has .. in them, run from beginning to end inclusively. The ranges which has ... in them, run exclusively the end value.

Ruby has a variety of ways to define ranges.

• Ranges as sequences
• Ranges as conditions
• Ranges as intervals

Iterator is a concept used in object-oriented language. Iteration means doing one thing many times like a loop.

The loop method is the simplest iterator. They return all the elements from a collection, one after the other. Arrays and hashes come in the category of collection.