Inconsistent handling of String columns

[Jammjammjamm]

According to the documentation, a column type of String corresponds to varchar(255). I have a migration which looks like this:

    create_table :headers do
      ...
      column :type, String
      column :name, String
      column :value, String
    end

When using sqlite, I get a schema like I would expect:

    create_table(:headers, :ignore_index_errors=>true) do
      ...
      String :type, :size=>255
      String :name, :size=>255
      String :value, :size=>255
    end

But when using postgres, these columns are converted to text:

    create_table(:headers, :ignore_index_errors=>true) do
      ...
      String :type, :text=>true
      String :name, :text=>true
      String :value, :text=>true
    end

[adam12]

But when using postgres, these columns are converted to text:

This is expected and documented on that page:

So while you specified String, Sequel will actually use varchar or text depending on the underlying database.

[Jammjammjamm]

I that case, I think it would be very helpful to also indicate that uncertainty in the code snippets in that section of the documentation, e.g.

String :a1                        # varchar(255)

-->

String :a1                        # varchar(255)/text (database dependent)

I can make a PR if that would be welcome.

[jeremyevans]

The heading of the section states # common database type used, and varchar(255) is the most common. If we were listing all possible specific database types that could be used for each generic type, that would result in quite cluttered examples.