Emacs, insert rectangular string interactively

Question

I often encounter situations in editing text or code where I want to insert a rectangle of spaces to align things, but I don't know exactly the number of spaces to insert.

For example, consider the following (very much contrived) snippet:

void *var = (void *)typedVar;
void *otherVar = voidStarOtherVar;
int intVar = x*y;
int intVar2 = y*z;

In default C-mode, M-x align results in this, which is better:

void *var      = (void *)typedVar;
void *otherVar = voidStarOtherVar;
int   intVar   = x*y;
int   intVar2  = y*z;

However, suppose my desired alignment (for some reason) is this:

void *var      = (void *)typedVar;
void *otherVar =         voidStarOtherVar;
int   intVar   =         x*y;
int   intVar2  =         y*z;

The only way I know to do that is with M-x string-rectangle on the bottom three lines, and type in the exact number of spaces.

However, I don't want to count the number of characters in (void *) before typing in the spaces, thus it would be nice to have an "interactive" rectangle string insert. For example, I type a space in this interactive mode, and I see it reflected immediately in the text. I enter another space, and it is inserted. In this way I can interactively align the text to my desired position.

Is there a built-in way to accomplish this? Or, failing that, can I create this functionality somehow?

Answer 1

Open rectangle may be useful for your example:

C-x r o' Insert blank space to fill the space of the region-rectangle (open-rectangle'). This pushes the previous contents of the region-rectangle to the right.

So you mark the desired rectangle, and this function will push content to the right of the rectangle.

Answer 2

Another alternative to those already presented is multiple-cursors on github, which is highly interactive and quite fun. There's a sublime Emacs Rocks! episode covering it on YouTube.