---
title: "String#concat, Array#concat & String#prepend Ruby 2.4"
description:
  "Ruby 2.4 now allows concat and prepend methods to take multiple arguments"
canonical_url: "https://www.bigbinary.com/blog/string-array-concat-and-string-prepend-take-multiple-arguments-in-ruby-2-4"
markdown_url: "https://www.bigbinary.com/blog/string-array-concat-and-string-prepend-take-multiple-arguments-in-ruby-2-4.md"
---

# String#concat, Array#concat & String#prepend Ruby 2.4

Ruby 2.4 now allows concat and prepend methods to take multiple arguments

- Author: Abhishek Jain
- Published: October 28, 2016
- Categories: Ruby 2.4, Ruby

In Ruby, we use `#concat` to append a string to another string or an element to
the array. We can also use `#prepend` to add a string at the beginning of a
string.

### Ruby 2.3

#### String#concat and Array#concat

```ruby

string = "Good"
string.concat(" morning")
#=> "Good morning"

array = ['a', 'b', 'c']
array.concat(['d'])
#=> ["a", "b", "c", "d"]

```

#### String#prepend

```ruby

string = "Morning"
string.prepend("Good ")
#=> "Good morning"

```

Before Ruby 2.4, we could pass only one argument to these methods. So we could
not add multiple items in one shot.

```ruby

string = "Good"
string.concat(" morning", " to", " you")
#=> ArgumentError: wrong number of arguments (given 3, expected 1)

```

### Changes with Ruby 2.4

In Ruby 2.4, we can pass multiple arguments and Ruby processes each argument one
by one.

#### String#concat and Array#concat

```ruby

string = "Good"
string.concat(" morning", " to", " you")
#=> "Good morning to you"

array = ['a', 'b']
array.concat(['c'], ['d'])
#=> ["a", "b", "c", "d"]

```

#### String#prepend

```ruby

string = "you"
string.prepend("Good ", "morning ", "to ")
#=> "Good morning to you"

```

These methods work even when no argument is passed unlike in previous versions
of Ruby.

```ruby

"Good".concat
#=> "Good"

```

#### Difference between `concat` and shovel `<<` operator

Though shovel `<<` operator can be used interchangeably with `concat` when we
are calling it once, there is a difference in the behavior when calling it
multiple times.

```ruby

str = "Ruby"
str << str
str
#=> "RubyRuby"

str = "Ruby"
str.concat str
str
#=> "RubyRuby"

str = "Ruby"
str << str << str
#=> "RubyRubyRubyRuby"

str = "Ruby"
str.concat str, str
str
#=> "RubyRubyRuby"

```

So `concat` behaves as appending `present` content to the caller twice. Whereas
calling `<<` twice is just sequence of binary operations. So the argument for
the second call is output of the first `<<` operation.

## Links

- [Human page](https://www.bigbinary.com/blog/string-array-concat-and-string-prepend-take-multiple-arguments-in-ruby-2-4)