```ruby
class String
  def set_param(placeholder, value)
    self.gsub("$[#{placeholder.to_s}]", value.to_s)
  end
end
```

Fix rubocop warning: redundant to_s in interpolation
user
```ruby
class String
  def set_param(placeholder, value)
    self.gsub("$[#{placeholder}]", value.to_s)
  end
end
```
assistant