Using "With" outside a function on its parameters [duplicate]

Question

I am making complex 3d graphics, and to clear up functions, I want to use With to remove a repeated action. This action occurs many times through many functions, so I want the With outside all of them, so I only declare it once. Except Mathematica doesn't seem to like having a With outside a function, if it is replacing parameters. A simplified version is shown below:

With[{y = x},
 draw[x_] := Cylinder[{{y,0,0}, {y+1,0,1}}, 0.1]
 ...(*other functions:See Bottom!!!!!!!!*)
]

then:

Graphics3D[draw[3]]

If I do the above, it brings the error:

So it should go y -> x -> 3. But it only gets half-way. It has changed y to x but I think it is after when the parameters are put in, so x is not changed to 3. Is there a way to keep the with outside, so it is only declared once.

Also, in case anybody says put the With before cylinder. No, I don't want to do that, as there are other functions using the values changed by "With"

-----------------------EDIT-----------------------------

The answers can replace the values for one function, as is shown in the code example, but it doesn't show (although I did say it), that it needs to work through many functions, as shown below. Sorry for the confusion, as causing the first two answers to not fully work.

With[{y = x},
 draw1[x_] := Cylinder[{{y, 0, 0}, {y + 1, 0, 1}}, 0.1], 
 draw2[x_] := Cylinder[{{y, 0, 0}, {y + 1, 0, 1}}, 0.2]
 ...(*more functions*)
]

Answer 1

There is a mismatch in your definition, between x and x$

draw // Information

Global`draw

draw[x$_]:=Cylinder[{{x,0,0},{x,0,0}},0.1]...

This is because With is a so called scoping construct. With tries to avoid conflicts between symbols. See this answer for a good explanation by Leonid. If you want to know all cases in which this happens, see this question by me.

If you wish to avoid such behaviour, you can use ReplaceAll on the outside, rather than With. There is another issue with your code too, as the two points in the first argument of Cilinder have to be different. So I have changed this. You could then use the following code

Unevaluated[draw2[x_] := Cylinder[{{y,0,0}, {y,0,1}}, 0.1]]/. Unevaluated[y->x]

Because the syntax with Unevaluated is a bit ugly, you may consider making your own function, like this.

SetAttributes[replaceWith, HoldFirst]
(*Unevaluated[y] is to make sure replaceWith works well when providing 
Unevaluated around its second argument*)
replaceWith[x_,y_]:= Unevaluated[x]/.Unevaluated[y]

The solution is then

replaceWith[
 draw2[x_] := Cylinder[{{y, 0, 0}, {y, 0, 1}}, 0.1]
 ,
 Unevaluated[y -> x]
 ]

In both cases, we have

draw2 // Information

Global`draw2

 draw2[x_]:=Cylinder[{{x,0,0},{x,0,1}},0.1]

Edit

You asked to make it work for multiple definitions. The solution is simply as follows

replaceWith[
 draw1[x_] := Cylinder[{{y, 0, 0}, {y + 1, 0, 1}}, 0.1];
 draw2[x_] := Cylinder[{{y, 0, 0}, {y + 1, 0, 1}}, 0.2]
 ,
 y -> x
 ]

Note that I have replaced a colon of yours by a semicolon. I prefer it this way, as this corresponds more closely to With (note that syntax in the example you provided was not correct). We then have

Graphics3D[{draw1[1], draw2[1]}]

Answer 2

When you do this, localization kicks in and renames one of the x to avoid conflict:

This is in general beneficial, and designed to prevent trouble. In some situations, however, you don't want this localization-through-renaming to happen. In that case you can use Replace instead of With to replace y by x.

I like to keep using the syntax of With though, so in these situations I tend to use the withRules function defined in the middle of this answer.

The caveat with withRules is precisely that it does not truly localize, so you need to be very careful when using it.

---

Update:

Version 10-specific template based solution:

template = (draw[x_] := Cylinder[{{#y, 0, 0}, {#y + 1, 0, 1}}, 0.1]) &

template[<| "y" :> x |>]

?draw

draw[x_]:=Cylinder[{{x,0,0},{x+1,0,1}},0.1]

Answer 3

You could also do this :

With[{y = x},
  SetDelayed @@ {Unevaluated[draw[x_]], 
    Unevaluated[Cylinder[{{y, 0, 0}, {y + 1, 0, 1}}, 0.1]]}
];