Why is the reference shallow-clone implementation so slow for low numbers of members to the trie?

[hughfdjackson]

At the moment, the benchmarks show it far too close to persistent-hash-trie implementations. I'd expect that shallow-clone would be WAYYYY slower.

assoc property with Trie of 1
//-------------------------//
shallow-copy reference  : 527,827.86 ± 3.77% ops/sec
v0.2.1                  : 733,140.34 ± 2.19% ops/sec
v0.3.1                  : 670,054.54 ± 2.18% ops/sec

assoc property with Trie of 10
//-------------------------//
shallow-copy reference  : 224,075.88 ± 1.51% ops/sec
v0.2.1                  : 379,912.96 ± 0.89% ops/sec
v0.3.1                  : 380,870.83 ± 1.90% ops/sec

assoc property with Trie of 100
//-------------------------//
shallow-copy reference  : 27,687.26 ± 1.47% ops/sec
v0.2.1                  : 103,969.98 ± 1.22% ops/sec
v0.3.1                  : 83,410.32 ± 2.33% ops/sec

assoc property with Trie of 1000
//-------------------------//
shallow-copy reference  : 2,765.97 ± 1.56% ops/sec
v0.2.1                  : 88,409.12 ± 1.15% ops/sec
v0.3.1                  : 58,476.34 ± 1.81% ops/sec

dissoc property with Trie of 1
//-------------------------//
shallow-copy reference  : 472,304.03 ± 2.00% ops/sec
v0.2.1                  : 500,163.65 ± 0.94% ops/sec
v0.3.1                  : 339,006.74 ± 1.33% ops/sec

dissoc property with Trie of 10
//-------------------------//
shallow-copy reference  : 234,291.83 ± 1.43% ops/sec
v0.2.1                  : 265,353.35 ± 0.97% ops/sec
v0.3.1                  : 231,454.93 ± 1.27% ops/sec

dissoc property with Trie of 100
//-------------------------//
shallow-copy reference  : 23,129.27 ± 1.14% ops/sec
v0.2.1                  : 104,765.06 ± 1.33% ops/sec
v0.3.1                  : 49,748.42 ± 0.90% ops/sec

dissoc property with Trie of 1000
//-------------------------//
shallow-copy reference  : 2,735.73 ± 1.25% ops/sec
v0.2.1                  : 66,539.11 ± 1.09% ops/sec
v0.3.1                  : 44,108.64 ± 1.41% ops/sec

has property with Trie of 1
//-------------------------//
shallow-copy reference  : 11,268,512.81 ± 0.95% ops/sec
v0.2.1                  : 9,996,323.62 ± 0.97% ops/sec
v0.3.1                  : 10,764,605.92 ± 1.10% ops/sec

has property with Trie of 10
//-------------------------//
shallow-copy reference  : 11,239,037.40 ± 0.96% ops/sec
v0.2.1                  : 8,848,967.81 ± 6.54% ops/sec
v0.3.1                  : 10,215,029.98 ± 1.16% ops/sec

has property with Trie of 100
//-------------------------//
shallow-copy reference  : 11,335,537.13 ± 1.10% ops/sec
v0.2.1                  : 4,965,439.67 ± 1.66% ops/sec
v0.3.1                  : 2,695,468.74 ± 0.82% ops/sec

has property with Trie of 1000
//-------------------------//
shallow-copy reference  : 9,988,683.47 ± 1.16% ops/sec
v0.2.1                  : 2,810,263.49 ± 1.61% ops/sec
v0.3.1                  : 2,860,534.34 ± 1.91% ops/sec

get property with Trie of 1
//-------------------------//
shallow-copy reference  : 33,840,663.32 ± 1.54% ops/sec
v0.2.1                  : 10,342,409.05 ± 0.94% ops/sec
v0.3.1                  : 11,718,582.12 ± 0.86% ops/sec

get property with Trie of 10
//-------------------------//
shallow-copy reference  : 35,464,325.40 ± 0.81% ops/sec
v0.2.1                  : 10,322,649.92 ± 0.98% ops/sec
v0.3.1                  : 11,385,616.80 ± 1.16% ops/sec

get property with Trie of 100
//-------------------------//
shallow-copy reference  : 35,888,018.23 ± 0.98% ops/sec
v0.2.1                  : 6,985,390.45 ± 1.13% ops/sec
v0.3.1                  : 4,127,919.22 ± 0.94% ops/sec

get property with Trie of 1000
//-------------------------//
shallow-copy reference  : 35,845,469.70 ± 1.03% ops/sec
v0.2.1                  : 2,360,341.90 ± 2.09% ops/sec
v0.3.1                  : 2,530,627.75 ± 1.10% ops/sec

mutable version of Trie with 1 members
//-------------------------//
shallow-copy reference  : 614,532.24 ± 1.55% ops/sec
v0.2.1                  : 345,559.32 ± 1.90% ops/sec
v0.3.1                  : 552,055.22 ± 7.75% ops/sec

mutable version of Trie with 10 members
//-------------------------//
shallow-copy reference  : 242,971.00 ± 1.13% ops/sec
v0.2.1                  : 74,049.34 ± 1.23% ops/sec
v0.3.1                  : 202,587.84 ± 1.57% ops/sec

mutable version of Trie with 100 members
//-------------------------//
shallow-copy reference  : 27,944.39 ± 2.23% ops/sec
v0.2.1                  : 4,836.35 ± 1.45% ops/sec
v0.3.1                  : 9,618.62 ± 1.47% ops/sec

mutable version of Trie with 1000 members
//-------------------------//
shallow-copy reference  : 2,813.12 ± 1.23% ops/sec
v0.2.1                  : 273.59 ± 2.28% ops/sec
v0.3.1                  : 879.25 ± 1.80% ops/sec

keys of Trie with 1 members
//-------------------------//
shallow-copy reference  : 11,214,744.36 ± 0.89% ops/sec
v0.3.1                  : 1,060,349.34 ± 0.77% ops/sec

keys of Trie with 10 members
//-------------------------//
shallow-copy reference  : 530,363.78 ± 1.15% ops/sec
v0.3.1                  : 103,964.29 ± 1.15% ops/sec

keys of Trie with 100 members
//-------------------------//
shallow-copy reference  : 64,794.20 ± 1.51% ops/sec
v0.3.1                  : 12,865.80 ± 1.83% ops/sec

keys of Trie with 1000 members
//-------------------------//
shallow-copy reference  : 6,164.72 ± 1.15% ops/sec
v0.3.1                  : 1,158.38 ± 1.35% ops/sec