Clojure

inconsistent numeric comparison semantics between BigDecimal and other Numerics

Details

  • Type: Defect Defect
  • Status: Closed Closed
  • Priority: Major Major
  • Resolution: Completed
  • Affects Version/s: Release 1.4, Release 1.5
  • Fix Version/s: Release 1.6
  • Component/s: None
  • Labels:
  • Patch:
    Code and Test
  • Approval:
    Ok

Description

BigDecimal does not have consistent comparison semantics with other numeric types.

user> *clojure-version*
{:major 1, :minor 5, :incremental 1, :qualifier nil}
user> (== 2.0 2.0M)
true
user> (== 2 2.0M)
false                  <-- this one is not like the others
user> (== 2 2.0)
true
user> (== 2N 2.0)
true
user> (== 2 (double 2.0M))
true
user> (== 1.0M 1.00M)
false    ;; potentially surprising

Patch: clj-1118-v7.patch

Approach: Change equiv for BigDecimals so that instead of using BigDecimal.equals(), it uses BigDecimal.compareTo() and checks the return value is equal to 0.

The javadoc for these methods explicitly states that BigDecimal.equals() will treat values that are otherwise equal numerically, but differ in scale, as not equal. They also say that BigDecimal.compareTo() will return 0 for such BigDecimals.

Doing this also changes the behavior of = when comparing BigDecimal values to other numbers. hash should be consistent with =, so now hash should return the same value for all numerically equal BigDecimal values. This patch modifies hasheq() to return the same value for all numerically equal BigDecimal values, by calling BigDecimal.stripTrailingZeros() on them before hashing. This change also will make 1.0M == 1.00M which was not true before.

Screened by: Alex Miller

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  • Created:
    Updated:
    Resolved: