torvalds

The linked list example

Linus Torvalds showed two ways to remove a node from a singly linked list.

Without taste (the standard textbook approach):

void remove(list *head, list *target) {
    list *prev = NULL;
    list *cur = head;
    while (cur != target) {
        prev = cur;
        cur = cur->next;
    }
    if (prev)
        prev->next = cur->next;
    else
        head = cur->next;
}

The if (prev) branch exists because the head node has no predecessor. Removing the first element is a special case: instead of patching the previous node's next pointer, you must patch the head pointer itself. Every reader of this function has to understand that the head is different from every other node, and that this branch handles it.

With taste:

void remove(list *head, list *target) {
    list **pp = &head;
    while (*pp != target)
        pp = &(*pp)->next;
    *pp = target->next;
}

The indirect pointer pp always points to the next field that refers to the current node. For the head, pp points to head itself. For every other node, pp points to prev->next. The assignment *pp = target->next patches whichever pointer was referring to the target, whether that was head or some node's next field.

The special case disappeared. Not because we handled it elsewhere, but because we chose a representation where head and non-head are the same. The branch was never necessary. It was an artifact of the data structure choice (prev pointer), not of the problem.

Why the first version is bad code:

1. The branch doubles the mental load. A reviewer must verify both paths are correct and that the condition is right.
2. The branch is easy to get wrong. Off-by-one in the prev == NULL check, or forgetting to update head, are common linked-list bugs.
3. The branch doesn't scale. If you add a tail pointer, you need another special case. The indirect-pointer version handles it with zero additional code.

The principle

Before adding a conditional, flag, mode, or special case, ask:

Can I change the representation so the special case doesn't exist?

If yes, change the representation. If no, document why the special case is irreducible.

Techniques

1. Change the data to remove the branch

The linked list example uses an indirect pointer. The general pattern: if two cases differ only in which variable you update, introduce a level of indirection that unifies them.

Database example: a query builder has separate paths for "first condition" (no AND prefix) vs "subsequent conditions" (needs AND). Fix: always emit WHERE 1=1 as a sentinel, then every condition is AND .... The sentinel eliminates the first-condition special case.

Config example: a function has separate code paths for "default config" vs "user-provided config". Fix: make the default config a real config value, not a nil/absent sentinel. Load defaults first, overlay user config. One code path.

2. Change the algorithm to remove the branch

If an algorithm has a special exit condition for one mode, ask whether a single algorithm handles all modes.

Convergence example: a migration loop exits differently for "converging" (dirty set shrinking) vs "diverging" (dirty set growing) workloads. Fix: one priority-ordered convergence check that handles both. The diverging case is just another criterion in the same list, not a separate code path.

Retry example: a function retries on transient errors but fails immediately on permanent errors. Instead of if is_transient(err) { retry } else { fail }, use a retry policy that maps each error to a delay: transient errors get backoff delays, permanent errors get delay zero (which means no retry). One loop, no branch.

3. Change the scope to remove the branch

If a caller has to choose between two versions of a function, ask whether one version handles both cases.

Filtering example: a function takes a skip_empty flag that changes which items it processes. Fix: make the function always filter empty items. If every item is non-empty, the filter is a no-op. No flag needed; callers don't choose.

Optimization example: a function takes a use_fast_path flag. Fix: make the function always use the fast path when applicable and fall back to the slow path otherwise. The caller doesn't decide; the function inspects its own data.

4. Make illegal states unrepresentable

If a runtime check guards against an invalid state, ask whether the type system can prevent that state from existing.

Enum over boolean: fn connect(tls: bool, verify: bool) has 4 states, but tls=false, verify=true is nonsensical. Fix: enum Security { None, Tls, MutualTls } — 3 states, all valid.

Newtype over primitive: fn transfer(from: u64, to: u64) can be called with arguments swapped. Fix: AccountId(u64) newtype prevents transfer(to, from) at compile time.

Builder over option soup: a struct with 5 optional fields where only certain combinations are valid. Fix: a builder that enforces the valid combinations at each step. Invalid states are unreachable.

When special cases are real

Not every branch is eliminable. The test: can you write a data structure, type, or algorithm that handles both cases uniformly? If no, the branch reflects a genuine domain distinction.

Examples of irreducible special cases:

• First iteration of a loop (no prior state to compare against)
• Root of a tree (no parent to notify)
• Network partition handling (fundamentally different from local errors)
• Platform-specific code (#[cfg(target_os = "linux")])

These are named, documented, and tested. They're explicit match arms, not hidden if branches buried in helper functions.

The heuristic

Count the if statements in your function. Each one is a branch the next reader must understand. If you can reduce the count by changing the representation, do it. If every branch is irreducible, the function is as simple as it can be.

Good taste is not cleverness. It is the discipline to find the representation where the special cases disappear.