clojure.core/subs should use type hints of ^CharSequence, NOT ^String

Tue, 13 Jan 2026 18:10:48 +0000

This is related to this ancient ask, but it would be ideal if clojure.core/subs was type hinted with ^CharSequence rather than ^String, and used the subSequence() method instead of substring() (since the latter doesn't exist in CharSequence).

The single parameter version of subs would need to call s.length() as the second argument in the call to subSequence() (there is no single-arg version of that method, unlike substring()).

More generally, there are substantial benefits in using CharSequence instead of String throughout Clojure core, not only in the context of Java interop, but also when using custom String-like data structures (e.g. ropes).

[edit] @alexmiller mentioned this in another forum (and I'm capturing it here for posterity), but this might also require that the result be stred, to ensure the return type remains unchanged (subSequence() returns a CharSequence, unlike substring, which might break callers). There may be performance implications of adding that call for types other than String (but existing callers should be unaffected, since String.toString() is identity).

cannot call Java Constructor overload

Mon, 03 Nov 2025 18:05:31 +0000

Jetty's BlockingArrayQueue has these two constructors (among a bunch of others):

/**
 * Creates an instance with given initial and max capacities.
 *
 * @param capacity the initial capacity
 * @param growBy the growth factor
 * @param maxCapacity the maximum capacity
 * @deprecated the growth factor isn't used anymore
 */
@Deprecated(since = "12.1.2", forRemoval = true)
public BlockingArrayQueue(int capacity, int growBy, int maxCapacity)
{
    this(capacity, maxCapacity, false);
}

/**
 * Creates an instance with given initial and max capacities.
 *
 * @param capacity the initial capacity
 * @param maxCapacity the maximum capacity
 * @param ignored this parameter is ignored but is needed as there is already a
 *  {@link BlockingArrayQueue#BlockingArrayQueue(int, int) deprecated constructor} that takes two ints.
 */
private BlockingArrayQueue(int capacity, int maxCapacity, boolean ignored)
{
    if (capacity < 0 || maxCapacity < 0 || capacity > maxCapacity)
        throw new IllegalArgumentException();
    _elements = new Object[capacity];
    _maxCapacity = maxCapacity;
}

I'm trying to call the second (the one with the boolean arg in the third position) but the compiler is hell bent on calling the first one.

(BlockingArrayQueue. 10 5 true)
Execution error (ClassCastException) at user/eval7644 (form-init275792826230635171.clj:1).
class java.lang.Boolean cannot be cast to class java.lang.Number (java.lang.Boolean and java.lang.Number are in module java.base of loader 'bootstrap')

(BlockingArrayQueue. 10 5 (boolean true))
Execution error (ClassCastException) at user/eval7648 (form-init275792826230635171.clj:1).
class java.lang.Boolean cannot be cast to class java.lang.Number (java.lang.Boolean and java.lang.Number are in module java.base of loader 'bootstrap')

(BlockingArrayQueue. 10 5 Boolean/TRUE)
Execution error (ClassCastException) at user/eval7652 (form-init275792826230635171.clj:1).
class java.lang.Boolean cannot be cast to class java.lang.Number (java.lang.Boolean and java.lang.Number are in module java.base of loader 'bootstrap')

What am I doing wrong?

Clojure Q&A - Recent questions tagged java interop

clojure.core/subs should use type hints of ^CharSequence, NOT ^String

cannot call Java Constructor overload