apache/iceberg · error · IllegalArgumentException

Cannot set value

Error message

Cannot set value 

What it means

Pair.put is a StructLike positional setter that only accepts positions 0 (first) or 1 (second). Passing any other index is an API contract violation, so it throws IllegalArgumentException with the offending index and value.

Source

Thrown at core/src/main/java/org/apache/iceberg/util/Pair.java:76

  private X first;
  private Y second;

  private Pair(X first, Y second) {
    this.first = first;
    this.second = second;
  }

  @Override
  @SuppressWarnings("unchecked")
  public void put(int i, Object v) {
    if (i == 0) {
      this.first = (X) v;
      return;
    } else if (i == 1) {
      this.second = (Y) v;
      return;
    }
    throw new IllegalArgumentException("Cannot set value " + i + " (not 0 or 1): " + v);
  }

  @Override
  public Object get(int i) {
    if (i == 0) {
      return first;
    } else if (i == 1) {
      return second;
    }
    throw new IllegalArgumentException("Cannot get value " + i + " (not 0 or 1)");
  }

  @Override
  public Schema getSchema() {
    if (schema == null) {
      this.schema = SCHEMA_CACHE.get(Pair.of(first.getClass(), second.getClass()));
    }
    return schema;

View on GitHub (pinned to 86d9c8fc54)

Solutions

1. Only call put with index 0 or 1
2. Use the first()/second() accessors or the Pair.of factory instead of positional access
3. Fix the loop bound in generic StructLike handling code to use the record's size

Example fix

// before
pair.put(2, value); // throws
// after
pair.put(value instanceof Integer ? 0 : 1, value);

if (pos < 0 || pos > 1) throw new IllegalArgumentException("Pair position must be 0 or 1, got " + pos);

boolean isValidPairPosition(int i) { return i == 0 || i == 1; }

try { pair.put(pos, v); } catch (IllegalArgumentException e) { /* log index and fix caller */ }

When it happens

Trigger: Calling put(int pos, Object value) on a Pair with pos outside {0,1}, e.g. from generic StructLike code that assumes a different arity.

Common situations: Generic structural-copy code iterating over field counts that doesn't match Pair's fixed 2-field schema; reflection-based writers.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Cannot get value
• Can't retrieve values from an empty struct
• Can't modify an empty struct
• Cannot set fields in a TypeProjection
• Setting values is not supported

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/f9ad915f4026f975. Report an issue: GitHub.