CODEWITHSUNDEEP
ruby-on-railsrubyconditional-statements
Fellow Stranger
Fellow Stranger

Reputation: 34053

Why does the conditional care about the execution code despite not returning true?

I have this code conditionally displaying the project's title if we're in a view that has the @project instance variable:

<title>My app <%= "- " + @project.title if @project.present? %></title>

But it gives me an error with the following message: "can't convert nil into String", i.e. it tries to execute my string concatenation despite the conditional statement being false.

Why does it even bother?

Upvotes: 0

Views: 39

Answers (1)

Simone Carletti
Simone Carletti

Reputation: 176472

You check if a project is present

@project.present?

but you don't check if the value of its title property is set. When title is nil, the following concatenation

"- " + @project.title

will fail with the can't convert nil into String error because you are effectively trying to concatenate

"- " + nil

that are two different types. You must deal with this case explicitly or use nil-to-string casting by using the interpolation

<%= "- #{@project.title}" if @project.present? %>

Moreover, beware of precedences. Embedding if conditions in that way with a print, may lead to obscure bugs caused by evaluation precedence.

Upvotes: 2

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