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Ruby provides a feature called string interpolation that lets you substitute the result of Ruby code into the middle of a string.
Ruby provides a feature called string interpolation that lets you substitute the result of Ruby code into the middle of a string.
- Interpolation works within double-quoted Ruby strings.
- Anywhere you want within the string, you can include an interpolation marker. A marker consists of a hash mark (also known as a pound sign), an opening curly brace, and a closing curly brace:
#{} - You can include any Ruby code you want between the curly braces.
- The code will be evaluated, the result will be converted to a string, and the resulting string will be substituted for the interpolation marker within the containing string.
- Lets us concatenate values like numbers with strings.
- Lets us embed simple math operations.
- Lets us embed the values of variables.
- We can include multiple interpolation markers into a single string.
- No interpolation in single-quoted strings.
$ irb
2.3.0 :001 > "aaa #{Time.now} bbb"
=> "aaa 2017-09-02 19:12:52 -0700 bbb"
2.3.0 :002 > "a string #{1}"
=> "a string 1"
2.3.0 :003 > "The answer is #{1 + 2}"
=> "The answer is 3"
2.3.0 :004 > name = "Jay"
=> "Jay"
2.3.0 :005 > "Hello, #{name}!"
=> "Hello, Jay!"
2.3.0 :006 > "#{Time.now} #{name}"
=> "2017-09-02 19:15:08 -0700 Jay"
2.3.0 :007 > 'Hello, #{name}!'
=> "Hello, \#{name}!"
Widget store code
- Let's try improving our widget store code using string interpolation.
- We'll remove the plus signs to combine all the concatenated strings into one.
- In their place, we'll add an interpolation marker that inserts the value of the
answervariable:puts "You entered #{answer} widgets" - It's easy to remember to put spaces surrounding the interpolation marker because it would look funny if we didn't.
def ask(question)
print question + " "
gets
end
puts "Welcome to the widget store!"
answer = ask("How many widgets are you ordering?")
puts "You entered #{answer} widgets"
You can see in the output that it's inserting the value of the answer variable into the string, and it's surrounded by spaces as it should be.
You entered 10
widgets
It still skips to a new line, which is a problem. We'll have an answer to that shortly.
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In order to avoid all these strings
being crammed together without any space
0:00
between, we have to
remember to add a space
0:03
to the strings on either
side of our answer variable.
0:06
This is a little awkward.
0:09
Another problem that we encounter with
string concatenation earlier is that if
0:10
you try to concatenate the string and
a number together, you'll get errors.
0:14
So if we were to take a string, and
try to concatenate a number with it, and
0:18
try to run this, we'll see
an error down here at the bottom.
0:23
Ruby provides a feature called
string interpolation that lets you
0:35
substitute the result of Ruby
code into the middle of a string.
0:39
Interpolation can address
these problems and more.
0:43
Let's go to our console and
launch irb, and
0:46
let's try interpolating
a value into a string.
0:49
Interpolation works only within
double quoted Ruby strings.
0:52
Anywhere you want within a string,
you can include an interpolation marker.
0:56
A marker consists of a hash mark,
1:00
also known as pound sign, an opening
curly brace, and a closing curly brace.
1:02
So let's close out the string here and
try running this.
1:09
And you can see that the interpolation
marker was removed from the finish string.
1:13
You can include any Ruby code you
want between the curly braces of
1:18
an interpolation marker.
1:22
So let's include
the method called Time.now
1:26
here in this interpolation marker,
close out the string.
1:31
The code within the interpolation
marker will be evaluated.
1:34
The result will be converted to a string,
and the resulting string
1:37
will be substituted for the interpolation
marker within the containing string.
1:40
So you can see we have the start
of our string here, and
1:45
then we have the result of Time.now
before the string finishes out.
1:48
String concatenation lets us easily
concatenate values like numbers together
1:53
with strings.
1:57
So let's say string put in interpolation
marker into the middle of it, and
1:58
we can include the number
1 without any problems.
2:02
It also lets us embed simple
math operations within a string.
2:06
So we could say the answer is,
2:10
And include an interpolation
marker with the operation 1 + 2.
2:16
Close out the string, and
we get the answer is 3.
2:21
interpolation is also an easy way
to insert the values of variables.
2:25
So let's say we had a name
variable that is set to "Jay",
2:29
we could interpolate that into a string
with Hello interpolation marker,
2:33
the variable name, and close out
the string, and we get "Hello Jay!".
2:39
We can include multiple interpolation
markers into a single string.
2:46
So we can say, #{Time.now},
2:50
followed by the value of #{name}, and we
get the two together as a single string.
2:53
If you ever actually want to include pound
signs and curly braces in your output,
3:01
you can use single quoted
strings to quote them literally.
3:06
So if we were to say Hello #{name} and
end the string,
3:09
we'll see those literal
characters within the output.
3:14
As usual, when you're ready
to exit irb and type exit and
3:19
press Enter,
you'll be returned to the system prompt.
3:23
Let's try and improving our widget
store code using string interpolation.
3:26
We'll remove the plus signs to combine
all the concatenated strings into one.
3:30
In their place,
3:35
we'll have an interpolation market that
inserts the value of the answer variable.
3:36
It's easy to remember to put spaces
surrounding the interpolation marker,
3:42
because it would look
funny if we left them out.
3:46
Let's try saving this and running it.
3:49
And you can see in the output that
it's inserting the value of the answer
3:56
variable into the string, and it is
surrounded by spaces as it should be.
4:00
But, why does it skip to a new line here?
4:06
To figure that out,
4:09
we're going to need to take a closer look
at the value of the answer variable.
4:09
And for that, we'll need to take
a brief detour in the next video.
4:13
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